Talk:Metric prefix

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Proposed Extensions[edit]

I altered the OP's post stating, "Of these only the litre is still in ubiquous(sic) use." In my experience, what the OP defines as an "are" is known as a(n) "hectare", that being an area equal to 56,000m2[1] (100mx100m). This term is used VERY widely as a pseudo-SI alternative to "acre" when talking about land and must, I would think, qualify as being in "ubiquitous" use? Also according to Google[2], an "are" is 1/100th of a hectare, or 10m2. As a result of this supporting evidence, I also altered the relevant parts of the post to reflect these values. 17:49, 21 March 2006 (UTC)

I'm not quite sure of where your figure of 56000 m2 comes from. It doesn't seem to have influenced anything in the article, so there's no harm done. Obviously 100 m x 100 m is 10000 m2 = 1 hectare. Yes, an "are" is an area of 100 m2, and is used in Spain for measuring the floor space of buildings.--King Hildebrand 16:50, 2 August 2006 (UTC)
That arithmetic is insane. 100 x 100 = 10,000, and 1 hectare is "equal to 10,000 square metres (104 m2)". --Thnidu (talk) 03:48, 8 February 2015 (UTC)


The article claims that a liter is sometimes "referred to as a 'dumphrey'". I couldn't verify that claim and removed it. AxelBoldt

Binary prefixes[edit]

The powers of two have a new SI standard, IINM. 210 bytes == 1 Kibibyte (1 KiB), 220 bits == 1 Mebibit (1 Mib), 230 bytes = 1 Gibibyte (1 GiB). -- Hari (2002-03-18)

See, for instance -- Hari (2002-03-18)

Could you add an explanation to that effect? Such as "KiB should be used instead of KB...". (It's not a SI standard however.) AxelBoldt

Does anyone have an objction to me moving most of the explanation of byte prefixes to Byte prefixes, and leaving just a short paragraph on it here & a link? -- Tarquin 14:45 Jan 12, 2003 (UTC)
I've renamed it to "Binary prefixes". It's used for anything based on the power of 2 (e.g., bits, words), not just bytes. -- Dwheeler 20:12 21 May 2003 (UTC)

In my opinion, the whole "Computing" section must go. It is entirely incorrect when using the rules of the SI. The SI does not define any special exceptions to do with computing, and this entry implying such is incorrect. It's fine if we move this to a new entry, but it must be very clear that such usage goes against the SI. --Eliasen 11:07, 28 Nov 2004 (UTC)

I agree. Remove the section and direct them to binary prefix. - Omegatron 22:36, Mar 3, 2005 (UTC)

A vote has been started on whether Wikipedia should use these prefixes all the time, only in highly technical contexts, or never. - Omegatron 14:56, July 12, 2005 (UTC)

"iso" prefix[edit]

I've just added this. Gritchka I have to say I've never seen 'iso' mentioned in this context. What's the authority for this?

I've never heard of it. My encyclopedia doesn't give it in the table of SI. Official reference such as doesn't give it. The only link I have found on google about it seems contentious (Star Trek science). It's also faintly ludicrous -- a metre is a metre. What is the point of saying "isometre"? Just to clinch it, the official site makes no mention of it. I think someone thought "isobar" was a prefix applied to "bar", whereas it's a line of constant value on a map. In short, I can't find any evidence of its existence, rather, I'm finding evidence of its non-existence. It's going. It's gone ;-) -- Tarquin 00:34 Sep 15, 2002 (UTC)
Or somebody was mistaking a mention of the ISO (International Standards Organization) for a prefix. --Thnidu (talk) 03:49, 8 February 2015 (UTC)

Subdividing these?[edit]

It's all very well with the prefixes given here, but what about for example organic chemistry? You require extra endings for 2, 3, 4, 5, 6... (Okay, so they start meth- eth- prop- but-, but that's not the point... think about silanes.) What are the prefixes for 1, 2, 3, 4, 5...?

I don't understand your question. There are only prefixes for powers of 10. The prefixes used for systematic chemical names have nothing to do with SI -- Tarquin 23:04, 2 Oct 2003 (UTC)
No one ever answered the OP's question, and since it's almost been a decade... an appropriate "metric like multiple" of the year (or the 'ade'?)... Silanes sequence similarly to methane, ethane... by using silane, disilane, trisilane, tetrasilane, pentasilane... at which point they use the same prefixes as the alkane series there once you reach penta. —Preceding unsigned comment added by (talk) 15:48, 31 March 2010 (UTC)

"Billiard", etc[edit]

Do the number names "billard", "trilliard", etc, really exist? "Milliard" is old-fashioned (possibly archaic) in UK usage although its cognates are current in some European languages. I have never seen "billiard", etc, listed in any printed dictionary, except as "billiards", which is a game similar to pool. The UK, as has been pointed out on the page, now tends to use "billion", etc, in the same way as they are used in the UK. Other European languages vary between the US system and the older UK system. Could someone point out an authoratitive reference that lists these terms? If not, could I suggest they are removed or marked as neologisms, for the nonce, rare, jokey, or something else? Thanks. -- Paul G 09:57, 12 Jan 2004 (UTC)

At least in Swedish, the series Miljon, Miljard, Biljon, Biljard etc. series is used.
Mark these old-fashioned possibly archaic words as neologisms, 'ay? You can't have it both ways. Yes, they do exist though, alas, rarely used in English these days. My vote would be to leave them in. The reason: the original naming system of numbers (what Wikipedia calls the long scale) is logical and therefore easier to understand especially for speakers of other European languages. Jimp 13Oct05
You can indeed have it both ways. "Milliard" is unknown in US English and archaic in UK English. "Billiard", "Trilliard", etc. are simply not English words, despite being used in other European languages. Other than tables of names of numbers you will be hard pressed to find these terms in either modern or historical English sources. —Preceding unsigned comment added by (talk) 20:27, 27 May 2010 (UTC)
As an American living in the Netherlands and working with Dutch and German co-workers, I run into the "billion/biljoen problem" somewhat regularly. Keeping the SI Prefix chart with both the "short scale" and the "long scale" is a very useful reference when crossing in and out of english while talking about big numbers. In "long scale" (what my co-workers natively think in) 1000000^1 is a million, 1000000^2 billion, 1000000^3 is a trillion, thus the prefixes match the exponents of 1000000. In short scale 1000^3 a billion, 1000^4 is a trillion, 1000^5 is a quadrillion, which strikes some of my non-american co-workers as strange because the prefixes don't seem to match the exponents. I would suggest the chart could be improved by adding a "1000000 to the X" column. That might really demonstrate the straight-forward logic of the "SI long scale" to us "short scale" readers and also show the "off by one" with the short scale (something I didn't understand until working with "long scale" thinkers for a little while). EricHerman (talk) 10:23, 1 October 2008 (UTC)

Another view:

Nature, it seems, is the popular name
For milliards and milliards and milliards
Of particles playing their infinite game
Of billiards and billiards and billiards.
—Piet Hein, in Grooks (1966).

--Thnidu (talk) 01:30, 15 August 2016 (UTC)

All these fighting over -illion or -iard are meaningless and off-topic because the prefixes are in 10^3 steps only and regardless only their order is important. There should be no misunderstanding of their scale at all even if they have different terms in different languages. That's the whole point of the system, too. Mightyname (talk) 20:03, 7 January 2017 (UTC)

Nonna, Dogga, etc.[edit]

Is there any reason that Nonabyte and Doggabyte haven't been added to this list yet? I was going to add them myself, but I wanted to clarify that their British name would be "Thousand Quadrillion" and "Quintillion", and that their symbols would be 'N' and 'D'. Does anyone have any authoritative sources on these? -- DropDeadGorgias 17:16, 19 Feb 2004 (UTC)

Because they are not real SI prefixes? -- The Anome 06:00, 1 Apr 2004 (UTC)

To answer this question about Nona and Dogga, there have been various times in history when nonabyte existed as a Wikipedia article, but it always went onto the "votes for deletion" page. About 90% of all Wikipedians agree that it shouldn't have a Wikipedia article. 02:01, 1 Apr 2004 (UTC)

There is a place for Non-SI unit prefixes. Why not put these there? Jimp 13 October 2005

Prefixes for 10^27 and 10^30[edit]

The creator of the Names of large numbers article has a part that uses SI prefixes for part of it that goes past yotta for xenna and viki. 23:13, 3 Jun 2004 (UTC)

Prefix for 10^27??[edit]

I contacted the webmaster of and they say that they will not confirm a prefix for 10^27 as of 2005. Any comments?? 16:29, 2 Jul 2004 (UTC)

Surely the entry for Bronto must be removed until such time as this is confirmed by SI / BIPM?
The BBC has just written an article mentioning Brontobyte [[3]] as 10^27, but, Googling, there seems to be few precedents - a Sybase article [[4]](which can't even spell yottabyte); a UCL article [[5]] which puts a Brontobyte at 1000 Eb = 10^21 = Zettabyte?? An American article [[6]] which thinks that Brontobyte = Petabyte = 10^15 - and none of these cite any de jure authority. Does anybody know the origin for this proposed term?? Given the ambiguity, surely it has to go? Ian Cairns 23:00, 20 Sep 2004 (UTC)

Petition going around for 10^27 to be designated 'hella' [[7]] —Preceding unsigned comment added by (talk) 14:43, 7 July 2010 (UTC)

What is the proposed symbol for hella? —Preceding unsigned comment added by (talk) 20:39, 7 July 2010 (UTC)

"Hella" suggests the colloquial intensive "hell of a ___". In line with the degree of seriousness of the proposed prefix, for its symbol I propose ♆ (U+2646), the astronomical symbol for the planet Neptune. It represents the sea god's trident, but it's close enough to a pitchfork to stand for Hell as well. --Thnidu (talk) 02:46, 8 December 2016 (UTC)

I stumbled upon the use of 'bronto-' and 'geop-' on a page about HP's Machine: Pretty sure that's not enough to include them in the article but it's worth signaling.--Grondilu (talk) 01:28, 14 June 2014 (UTC)

These are all in Unit prefix#Unofficial prefixes. --Thnidu (talk) 03:54, 8 February 2015 (UTC)

But the next prefix must begin with an x though, bronto- and geop- don't begin with an x. There is a pattern at the end, zetta- and yotta- have their letters as Z and Y. Same with yocto- and zepto- their letters are z and y, the last 2 letters of the alphabet. So i don't really like the idea of bronto- and geop- that much, maybe xona- and xonto- would be a better option. (talk) 17:39, 16 April 2017 (UTC)

@ What you or I want or like or prefer are irrelevant. This article and page are not for proposing additions to the metric system, much less for listing our own or anybody else's made-up prefixes. Here we are dealing only with those prefixes that are listed in Standard ISO 80000-1.[1] If you want to find out or talk about others, go to Unit prefix § Unofficial prefixes and Talk:Unit prefix. --Thnidu (talk) 05:42, 19 April 2017 (UTC)


  1. ^ ISO 80000-1 Quantities and units. Part 1: General (1st ed.). Switzerland: ISO (the International Organization for Standardization). 2009-11-15. p. vi. Retrieved 23 May 2015.


According to billion and Fowler,* 'billion' can mean both 10^9 and 10^12 in the UK. Best to not mention it in the table headers -- Tarquin 08:57, 21 Sep 2004 (UTC)

The 10^12 meaning is utterly obsolete in the whole English-speaking world. As this is the English Wikipedia, the "long scale" column should really be removed to prevent needless confusion. – Smyth 13:02, 27 Sep 2004 (UTC)

Fowler is a DAB page. Tarquin almost certainly meant A Dictionary of Modern English Usage, originally by Henry Watson Fowler. --Thnidu (talk) 04:58, 25 April 2017 (UTC)

Bogus SI prefixes[edit]

The category Category:Bogus SI prefixes contains a whole bunch of stubs that look to me like they're unlikely to grow. Anyone object if I merge them all into Bogus SI prefix or something similar? Bryan 05:33, 14 Oct 2004 (UTC)


How popular of a belief is it that it is okay to use mega- as a numerical prefix for a million (as if it belonged in the regular Greek numerical prefixes article)?? It is not in there; its literal meaning is "great". 01:29, 31 Oct 2004 (UTC)

Never heard someone use it. Chemicals pentane, hexane, ...., mega-ane? No way, you'd call the latter simply polyethene. I can't think of a situation right now where it could be used. A numerical prefix suggests that it is exact (1,000,000 and not 1,000,002) which usually doesn't make much sense for big numbers. Han-Kwang (talk) 12:08, 16 Nov 2004 (UTC)
Megaton is used for an explosion equivalent to 1 million tons of TNT. Is this an example of what you mea, or have I got hold of the wrong end of the stick?--King Hildebrand 15:41, 2 August 2006 (UTC)
@Hankwang: I may be beating a (twelve years) dead horse, but people still read the Talk page so I'll go ahead: This article is about metric prefixes, that is, prefixes used in the metric system of units. It is not about numerical prefixes in general. Other uses of numerical prefixes, including the chemical terms you mention as well as bigamy, trilogy, tetrapod, hexagon, and decade, have no relevance here.--Thnidu (talk) 18:45, 4 May 2016 (UTC)
Time flies; have I been around for that long? :-) Han-Kwang (t) 07:51, 5 May 2016 (UTC)
@Hankwang: Time flies? You can't. They fly too quickly.--Thnidu (talk) 23:38, 5 May 2016 (UTC)
Megavolt and Megaohm are commonly used in electricity and electronics. Dhrm77 (talk) 14:33, 4 May 2016 (UTC)
@Dhrm77: "Megaohm" is pretty rare. Usually "megohm" is used instead. --Thnidu (talk) 18:10, 4 May 2016 (UTC)

What about a Megalith - just a big rock not a million of anything! (Chris Neale)

"Megalith" and chemical names are not relevant, and neither are "microphone" and "microscope", for that matter. This article is about (pay attention, now) prefixes for units of measurement. Yes, the literal Greek meaning of μεγα- mega- is "big", and that of μικρο- micro- is "small", and that of νανο- nano- is "dwarf". Which has absolutely no bearing on their adoption to mean "million", "millionth", and "billionth". --Thnidu (talk) 04:00, 8 February 2015 (UTC)


Do doctors in American medical soap operas always say "cc" (short for "cubic centimetre") to mean "millilitre" because they don't want the audience to know they're using a metric unit? At least here in Finland, "millilitre" is a much more widely known unit than "cubic centimetre", even though they're the same thing. JIP | Talk 17:17, 1 May 2005 (UTC)

No, all doctors in America use cc. Cburnett 17:25, May 1, 2005 (UTC)
Why do they call it cc instead of millilitres, then? JIP | Talk 18:52, 1 May 2005 (UTC)
I wouldn't tak that as an established fact based on one person's comments. For example, what specific context do you have in mind? Liquid drugs are usually labeled in milliliters, and so prescribed. What's used for capacity of syringes? For cranial capacity? The more prevalant usage can be different in different contexts.
You are probably just a kid who doesn't remember the days when we had to learn that milliliters and cubic centimeters are different units. Some of the usage habits today go back to those days when a distinction was sometimes made for clarity, even though very few measurements were ever precise enough to tell he difference. That's just one of the factors that come into play--but fooling the audience into thinking they are not using a metric units is one of the least plausible factors. Your theory doesn't hold any water. Americans know that it is a metric unit, whether it is "cc" or "cm³" or "mL". Gene Nygaard 19:23, 1 May 2005 (UTC)
Actually, I've even seen liquid drugs measured in miligrams. In particular, morphine. Measuring liquids in cc's and solids in mg's are probably the most prevalent. I've *never* had a prescription filled in grains or ounces. :) But whatever is used and why, it has little to do with "fooling the audience". Cburnett 22:46, May 1, 2005 (UTC)
Really? I'm sure it was expressed in milligrams per mL if you check again. —Preceding unsigned comment added by (talk) 04:15, 16 May 2009 (UTC)
If close to 30 years is "just a kid" to you, then I agree. But no, I don't remember ever learning that cubic centimetres and millilitres are any different. JIP | Talk 04:27, 2 May 2005 (UTC)
From 1901 until 1964, 1 ml was approximately 1.000028 cm³. The liter was then defined as the volume of one kilogram of water at its maximum density, rather than as a cubic decimeter.Gene Nygaard 04:40, 2 May 2005 (UTC)
Figures, seeing as I wasn't born in 1964. My parents hadn't even met each other then. The bit about fooling the audience was pure speculation on my part. JIP | Talk 14:48, 3 May 2005 (UTC)

An old man such as myself remembers that many of our American textbooks of the late 1940 to pre-1970 era distinguished them as: cc = volume, ml = capacity (the latter being contingent on positive, neutral or negative meniscus formation of liquids). I hope this is some help; Dr.R.E.Petrere

Non-standard prefix abbreviations?[edit]

What about non-standard abbreviations, such as "mc" or "u" for "micro"? --Carnildo 17:41, 20 Jun 2005 (UTC)

That's talked about at micro. Lee S. Svoboda 20:25, 7 October 2005 (UTC)
From micro: "In circumstances where only the Latin alphabet is available, the SI standard allows representation of the prefix using the letter u as in um for µm, or uV for µV." This assertion must be sourced or deleted. I didn't find this statement of this in SI Brochure ( so I think this use is not allowed officially. Please provide a source or it will be deleted. Armando82 11:04, 20 April 2007 (UTC)
I strongly feel it should be mentioned/noted that 'u' is used in some contexts as a replacement abbreviation for micro. Though it is not in the standard, it's widely used in reference to microfarads, especially on electronics hobbyist websites: [8] [9] [10] [11] and the writers assume that the reader will understand that 'u' means 'micro' in this context. It should definitely be noted, though, that this is not standard. (The same websites tend not to put spaces between the number and the unit, too--also nonstandard.) The belief that the 'u' abbreviation is standard may stem from the belief that the (withdrawn/retracted) ISO 2955 linked at the bottom of the article is part of the SI, which it isn't. (talk) 16:03, 1 July 2014 (UTC)

Merge with SI#SI prefixes[edit]

Shouldn't this be merged with SI#SI prefixes? They seem to have very similar contents.

Lee S. Svoboda 20:28, 7 October 2005 (UTC)

Yes, SI#SI prefixes should be moved here. The article SI is far too large as it is. Moving the bulk of SI#SI prefixes here would help make SI a more manageable size. Jimp 13Oct05
It's done. Jimp 14Oct05

History of the SI prefixes?[edit]

Does anyone have solid information on when the various SI prefixes were first introduced? I am under the impression that prefixes through mega/micro go back to the beginning of the Metric system, tera, giga, nano and pico go back to the intro of SI in 1960 (though they must have been discussed earlier) and the rest are newer (1980s??) . But it would be interesting to pin down dates and maybe add them to the table in the article. --agr 21:46, 18 December 2005 (UTC)

I'd love to know this, too. "Many SI prefixes predate the introduction of the SI in 1960." How far? — Omegatron 15:00, 24 February 2006 (UTC)

Deci, Centi, Milli[edit]

Deci, centi, and milli are the oldest prefixes. They first appeared in a report by the Commission on Weights and Measures in 1792.[12] A report in 1793 provided abbreviations for the prefixes and the units.[13]:

  • length: millaire --- metre - decimetre - centimetre - millimetre (abbreviated as: mt. - - -
  • area: are - deciare - centiare (ar. - -
  • volume: cade - decicade - centicade - cadil (cd. - - - cl.)
  • mass: bar - decibar - centibar - grave - decigrave - centigrave - gravet - decigravet - centigravet - milligravet (br. - - - gv. - d.gv. - c.gv. - gvt. - d.gvt. - c.gvt. - m.gvt.)
  • currency: livre - decime - centime (lv. - dm. - cm.)
(First use of the modern abbreviations m and mm for metre and millimetre that I found is 1819 by Fresnel)[14][15]
The prefixes deci-centi-milli are actually older because Mouton proposed them in 1670 as decimal submultiples of the virgula (approximately 1 foot): decima, centesima, and millesima.
Ceinturion (talk) 22:28, 17 September 2015 (UTC)


In 1793 the Commission on Weights and Measures recommended that decimal subdivisions of a millimeter are simply called tenth, hundredth and thousandth of a millimeter.[16] The prefix 'micro', its symbol µ, and the name 'micron', were invented later:

Who, on reading the microscopic literature, would at once have been able to estimate the proportions between e.g. 0.0075 mm, 1/302 Paris line, 0.000285 Viennese Zoll, and 1/3380 inch? All four are the same: about the size of a blood corpuscle. It is obvious that one could only read the literature with a reduction table in one's hand. Vulgar fractions were often too inaccurate; they also were difficult to handle when making calculations. On the other hand, decimal fractions were difficult to evaluate because of the many zero after the full stop. All microscopists in the 19th century complained about the metrological chaos, but nobody did anything about it; partly because each after all, found the notation to which he himself was accustomed the most usable, and partly because all were afraid of not being read any longer at all, if they introduced a new notation.
The first author who decided to choose the thousandth of a millimetre as a unit was Harting, in 1844, then professor of Zoology at Utrecht. In that year he called this unit millimillimetre, and a year later, in a detailed micrometric study, also micromillimetre. He abbreviated this to mmm.
Exactly ten years later -in 1854- it was the Dutch undergraduate W.R.F. Suringar who, in his response to a competition launched by Leyden University, replaced Harting's mmm "for the sake of convenience" by the letter µ. The manuscript remained unpublished, and is kept in the State Herbarium at Leyden. This denomination (µ) appeared in print three years later for the first time, in Suringar's thesis for his doctorate.
Harting did not follow this notation; he continued to use the abbreviation mmm. Nageli and Schwendener lent their authority to the name "Mikromillimeter", which they abbreviated to "Mik". Meanwhile the need for 1/1000 mm unit was being felt also in physics. The Göttingen Professor Listing wrote: "Ich nenne es Mikron oder Mikrum", and he indicates it by µ. As more countries introduced the metric system, the time also became ripe to insist on the international unification of microscopic measurement.
(Citation from: Actes for 5th-11th Congress issued as Collection de travaux de l'Académie internationale d'histoire des sciences, 1968).
Wavelengths of light, measured in the early 19th century, were much smaller than the millimeter, the smallest metric unit at the time. It is interesting to see the expression of wavelengths change from fractional to decimal (with a lot of leading zeroes), and from non-metric to metric: 1801 Young: red = 1/43636 of an inch [17], 1819 Fresnel: red = 0,000638 mm [18][19], 1823 Fraunhofer: red = 0.00002422 parts of a Parisian inch [20], 1829 Babinet: red = 0.00002425 parts of a Parisian inch = 0.0006565 millimetres [21], 1828 Herschel: red = 0.0000256 parts of an inch [22], 1846 Peschel: red = 6.502 ten thousandth parts of a millimetre, or 0.0006502 of a millimetre [23] Ceinturion (talk) 13:21, 23 October 2015 (UTC)

The earliest use of the prefix micro- (and mega-) for other units than metre that I found is 1868 in An Elementary Treatise on Electrical Measurement by Latimer Clark. He explained the prefixes, and used them in electrical units (megafarad, microfarad, megohm, microvolt). In 1874 the British Association for the Advancement of Science introduced the CGS system, including the prefixes micro and mega. Ceinturion (talk) 11:06, 2 August 2015 (UTC)


This term for 10^3 (1000) has existed since Greek has diverged from other Indo-European languages. The way Greek words normally come into English would have it be chilia, and the reason for the kilo spelling is unknown; I think it is disputed whether it is because ch can be pronounced differently by different languages, or whether they had centi- and didn't want the letter c to be ambiguous. Jimp 14Oct05

Well, according to this is an "innovation". Which means, they started from the greek but simplified the word thru usage of what the author (a person from the XIXth century) a "new orthograph" : replacement of "ch" by a "k". So, as a summary this is an innovative word for an new way of mesuring the amounts, the SI . BJB 13Jan2010 —Preceding unsigned comment added by (talk) 15:49, 13 January 2010 (UTC)
Some transcriptionists always used kh for the greek letter chi. So, that khilia gave rise to kilo is a rational explanation. The French digraph ch is an English sh, we'd have "shillo-meters". French c before i sounds as English s, we'd have "sillo-meters". Logically, the best way to keep a hard aspirated k sound is to use the letter k. It wasn't thus so innovative (talk) 15:55, 31 March 2010 (UTC).
The best source is Delambre (who measured the French meridian) who stated in his precise description of the metric system (1806) that the ch in chilio was replaced by a k to make sure that everyone would pronounce it as a k. [24] Ceinturion (talk) 11:48, 19 August 2016 (UTC)


This term, I think, was coined in 1874 by someone who thought an SI prefix was needed for 10^6. They knew Greek didn't have a word for a million, so they just decided to coin a term coming from a word meaning "great".

The first use of the unit prefix mega that I found is 1868, in An Elementary Treatise on Electrical Measurement for the Use of Telegraph Inspectors and Operators, by Latimer Clark. Electrical engineers were concerned with long-distance telegraphy, and the cardinal operation in electricity was the measurement of electric resistance. The megohm was convenient for measuring the insulation of undersea telegraph cables (70 megohms for 50 miles of cable) and insulators for overhead telegraph lines (4 megohm in rain, 100,000 megohm when dry). He did not need to invent mega as a prefix; he borrowed it from other domains, such as fossils and instruments.
In 1873, a new, coherent system of units, CGS, was introduced by an influential report of the British Association for the Advancement of Science (B.A.). The new system included a few prefix changes compared with the metric system. The new prefixes mega and micro were allowed for all unit names. A silent change was the removal of the prefix myria. Perhaps myria was removed to transfer its abbreviation M to the new prefix mega. Ceinturion (talk) 20:34, 14 August 2016 (UTC)

Giga and Tera[edit]

These terms were coined by extrapolating mega for great by including giga- for giant and tera- for monster, both from Greek.

Peta and Exa (the ones I think are absurd)[edit]

These terms are the ones I think are absurd because of how they originated. Do you hear stories like these??

Let's make up 3 characters named George Washinton, Thomas Jeffeson, and Benjamin Franlin. We made up these characters' names by taking names of famous people and dropping one letter out.

Then, a forger who stumbles across the story with the names falsifies the names by adding in the letter dropped out.

The people who coined these prefixes in 1975 must not have been thinking of these, but because this is how these prefixes came into existence, I regard them to be absurd!

This looks like a fascinating explanation, but I suspect it needs a bit of clarification. I, personally, can't see any link at all between the story and the prefixes. Sorry to be dim, and all that! Could someone (possible the original anonymous poster) please explain a little more fully? Many thanks. --King Hildebrand 13:53, 2 August 2006 (UTC)
Sorry - I think Georgia Guy's signature applies to the whole section. I'll go and ask him... --King Hildebrand 13:54, 2 August 2006 (UTC)

Peta was derived from Greek penta, five, with one letter missing because tera (10004) looked like tetra, four, with one letter missing. Exa was derived from Greek exi, six. (talk) 21:26, 18 February 2016 (UTC)

Zetta and Yotta[edit]

These were the start of a sequence in descending alphabetical order all SI prefixes from this onward are expected to follow. Georgia guy 00:13, 1 May 2006 (UTC)

And one other thing to say[edit]

  • The next preifx, starting with X, whether xona- or xena-, how should the X be pronounced?? Georgia guy 00:34, 1 May 2006 (UTC)

Here's a page that contains the dates of adoption of every prefix:

Kilo [k] 103, one thousand; (from the Greek word khilioi, meaning thousand). This prefix was one of the original six prefixes of the metric system, when it became official on 1 August 1793.
Mega [M] 106, one million; (from the Greek word megas, meaning large). This prefix was introduced by the BA (British Association for the Advancement of Science) as part of the CGS-system of units in 1874 when the new units for electricity and magnetism were standardized.

etc. Very good information that we should include in this article. — Omegatron 22:53, 9 June 2007 (UTC)



You should include the myriad prefix (abbr. is unknown to me)even if it is disambuigated. You should also note that the term now means "a lot," "many," and/or/any combonation of/with "much." I cant find much info. on it but maybe you/othres can.

This is already noted as myria- and/or myio-......

I have also found myria- as prefix for meter (in Hungarian: miriaméter) in a Hungarian law from 1874, which implemented the SI in Hungary. Since this law implemented international standard, myria must have been an official SI standard then.Timur lenk 00:43, 24 September 2006 (UTC)

I think you are confusing the metric system with the International System of Units, which is symbolized "SI" in every language. SI was developed in 1960, and one of the goals was to discard obsolete, redundant, and ill-considered units. Myria- was discarded at that time. It's metric, but it's not SI. --Gerry Ashton 04:30, 25 February 2007 (UTC)
Myria was removed much earlier, in 1873, by the adoption of the CGS system of units. Ceinturion (talk) 22:59, 14 August 2016 (UTC)

I dont know (Jiwe-)[edit]

Is it true that they used to have a unit called Jiwe-, I dont think so but it could be true. I think it was meant to be 1x10^3+.21/K (of same base unit)-13% of one uL. Quite complicated, huh.... I can see why they dropped it if it was evre used....

non-SI scales[edit]

"The reason various fields have develop their own non-SI scales is because of the problems posed by calculating very large or very small numbers on a computer accurately and efficiently. 1 angstrom is a lot easier for a computer to use in calculations than 1 × 10-10meter as truncation errors and rounding errors can occur losing accuracy in the calculation."

Speaking as a programmer, this is nonsense. Computers are very good at this sort of thing, and would work in floating point which would have no such limitations in the ranges spoken of. Also, the use of scaled units predates the wide use of computers, and may well be more historical than anything else. They may be inconvenient for people to work with, but that's a separate thing. I will remove this section. Notinasnaid 10:03, 1 June 2006 (UTC)

Giga pronounciation[edit]

[ˈgɪgə] and [ˈdʒɪgə]. The former is more common than the latter. How do you know this?Seforadev 03:55, 20 June 2006 (UTC)

Personal experience lends credence to the opinion in the article. I have been moving in scientific circles for forty or more years, and have very rarely heard the soft form, [ˈdʒɪgə], used. --King Hildebrand 13:44, 2 August 2006 (UTC)
I'm not a scientist, but I say 'gigabyte' with a hard G, and I have only ever heard it that way. The only time I've ever heard the soft one is in "1.21 gigawatts." (talk) 15:00, 1 July 2014 (UTC)


The term "micron" is, I believe, non-standard. The SI prefers "micrometre". Thus "millimicron", given as an unapproved usage of combined prefixes is not a good example. After all, if you remove the prefixes you are left with nothing but the letter N! Micron, along with thou (one thousandth of an inch) are used familiarly by engineers, and are not part of SI. --King Hildebrand 13:39, 2 August 2006 (UTC)

Abbreviations D and H[edit]

When I was a kid, and first learned of these prefixes and abbreviations, I was taught that the correct abbreviations were D for deka, to distinguish it from deci, and H for hecto. The exception, I was taught, from capitals indicating positive powers, was k for kilo. The SI came into existence (1960) around the same time as I learned this, so my teacher (my mother) was probably not influenced by the authorities in Paris. In fact, I don't think I ever encountered da for deka before reading this article! Deka is probably the least used prefix.--King Hildebrand 16:40, 2 August 2006 (UTC)

That would have been nice but it just ain't so. When "deka-" and "hecto-" were conceived they didn't imagine we'd go all the way up and down to "yocta-" and "yotto-". The capitals-for-positive-and-lower-case-for-negative-powers rule didn't come till later. Jimp 05:15, 4 August 2015 (UTC)
At the birth of the metric system, in 1795, lower case abbreviations were recommended for the prefixes myria, kilo, hecto, deca, deci, centi, milli: m k h d - d* c* m*.[25] Strangely, to avoid confusion, the prefix abbreviations marked with * had to be suffixed to the unit (for example, mg kg hg dg g gd gc gm), which apparently seemed like a bright idea during the French Revolution, but it wasn't a success. In the early years the abbreviations were rarely used, and a litttle later in the period of the mesures usuelles (1812 - 1840) the new unit names and their abbreviations were not needed. After 1840 capitalized 'big' prefixes (myria, kilo, hecto, deca) became popular: M K H D - d c m. After the introduction of the CGS system (1873) the prefix myria was abandoned and lowercase abbreviations for kilo, hecto and deca were favored.[26] [27] Deca was abbreviated by two letters, da or dk, to avoid confusion with deci. The new prefix mega was abbreviated with a capital M, so the new abbreviation series was M k h da/dk - d c m. The lowercase abbreviations were continued in the SI system in 1960, but the da/dk-ambiguity was removed, 'da' was chosen for deca. In summary, a capital D for deca was old-fashioned long before SI. Ceinturion (talk) 21:27, 16 August 2016 (UTC)


What is the correct form for deka? I think "k" is better than c, since the word derives from greek. Besides da, dk is also a common abreviation of deka (at least in the case of dekagram - dkg).Timur lenk 00:50, 24 September 2006 (UTC)

If you look at the the article's first external link, The International Bureau of Weights and Measures (BIPM): SI prefixes, you will see deca and da recommended. If you look at the third external link, US NIST "Definitions of the SI units: The twenty SI prefixes" you will see deka recommended, but the symbol recommendation is the same, da. So either is acceptable, but deka is preferred in the USA and deca is preferred elsewhere.
I live in the USA, and I don't recall ever seeing the deka prefix used, no matter how it is spelled. --Gerry Ashton 04:45, 24 September 2006 (UTC)
Thanks for the info. I live in Hungary and deka is commonly used in dekagram to measure mass in retail (typically sausage, cheese or such in a mall or grocery). The most widespread abbreviation is dkg, but very rarely dag can be seen as well. The form dkg is thaught in schools, too. Despite the practice in some other countries, grams are never used to measure mass (weight) in shops/groceries (you never ask for 300 g but for 30 dkg of cheese).
In an interwar Hungarian schoolbook (from the 1930s) I have seen deka as prefix of meter (forming dekameter), but it is totally unknown nowadays. Since the metric system was implemented by law in the 1870s, it can be an archaism - like myriameter (10 000 meter), which I have seen only in the above law.Timur lenk 10:10, 25 September 2006 (UTC)
Not unknown, but rather standard in US English. —Quondum 13:13, 3 April 2019 (UTC)

Kilo, why k and not K?[edit]

Just a question if anyone knows. Why does kilo use (small) k and not (big) K as the other larger than 0 units? It's the same with deca (da) and hecto (h) but they are a bit outside since they don't follow the tree step thingie, so I can accept them. But I feel kilo should be K. So, why isn't it?

I ask this question because MSWord wants it to be K but safe sources say k. —The preceding unsigned comment was added by Thavox (talkcontribs) 11:49, 6 March 2007 (UTC).

The way I was taught is that when abbreviating units a letter is captialized only when the unit is named for a person or some other proper noun. For example the unit of force Newton is named after Isaac Newton so it is capitalized as "N" while the unit of length meter that is not named for anyone or any specific thing is a lower case "m". So the torque unit Newton-meter as I have seen it is usually abbreviated as "N-m". Other examples of capitalized units are Farad "F", Celsius "C", Joule "J" and Fahrenheit also "F". All named after real people that made significant contributions to physics. Heat units other than the Joule are British Themal Unit that is commonly capitalized as "Btu" (sometimes BTU) and calories that are abbreviated lower case as "cal" follow this convention. These days it seems that many of the computer related units do not follow the old convention. The prefixes giga and mega as related to computer science are usually abbreviated as "G" and "M" respectively. Also I don't think there ever was a "Mr. Byte" that made any significant contribution to computer science but hard drive capacities are routinely measured in "GB" and "TB" instead of "gb" and "tb". I'm sure there are many other exceptions. Having learned things this way I have always looked upon capitalizing certain units as a way of honoring truely exceptional people that changed every one of our lives for the better. At this point in my life I can say that there probably will never be a unit named after me but I can say with absolute certainty that you will never see me abbreviate a Newton as a simple lower case n. —Preceding unsigned comment added by (talk) 05:16, 13 April 2008 (UTC)
The unit should be spelt newton, likewise it's kelvin, joule, farad, etc. degrees Celsius retains its capitalisation though. Degrees Fahrenheit is non-metric so the rule doesn't apply. The unit symbols are capitalised when named for a person and unit symbols not named for a person are generally not, however, there can be exceptions, the litre symbol, for example can be written as capital or lower case. The byte doesn't count since it's not a metric unit. However, that's the plain units we're talking about. The prefixes are a different story. Prefixes for a million and above are capitalised and those for less than a million are not. Why have the cut-off point somewhere between a thousand (or, more specifically, a myriad) and a million? That down to history, I s'pose they might have originally thought that 10,000 was large enough and 0.0001 small enough and decided to make all the prefix symbols lower-case, didn't think to revise it when they got to mega- and it ended up sticking. JIMp talk·cont 05:37, 5 June 2008 (UTC)
Anonymous "", the question was about abbreviating the prefix, not the unit name. A kilonewton, as many would write it, would still be abbreviated as kN. --Thnidu (talk) 04:06, 8 February 2015 (UTC)
I think it's just because K is the abbreviation of the unit kelvin for temperature; same with units meter and gram for the prefix M and G (even if there is the unit gauss for magnetic field and 1GG will be 1000000 gauss...). (talk) 11:47, 28 May 2019 (UTC)
The suggestion that the k prefix is lowercase because kK is better than KK for kilokelvin is an anachronism. Before 1954, the kelvin was °K (degree Kelvin), which is somewhat incompatible with a prefix (k°K?). Earlier, in 1932 an "official abbreviations of international metric units" document for the general public already said: "Metric abbreviations are simply the initial letters of the units combined with the initial letters of the prefixes, set solid in lower case". Interestingly, the document only mentions the common prefixes milli up to kilo, and the units meter, gram, liter, are. This rule suggests the purpose was to expose the general public only to fully lowercase units, and to confine (fully or partially) uppercase units to scientists. Ceinturion (talk) 18:10, 30 May 2019 (UTC)

Excessive use of symbols[edit]

User: AnyFile recently revised the lead paragraph to avoid using spelled-out units and prefixes when preceded by a number. AnyFile stated that such usage was "not allowed by SI rules." I have seen style guides that encourage the use of symbols in scientific writing, but I am not aware of the prohibition mentioned by AnyFile in any publication that has the force of law. Furthermore, I believe spelling out the units is appropriate in a paragraph that is introducing readers to the concept of SI prefixes, advice in any style guide notwithstanding. --Gerry Ashton 14:03, 4 April 2007 (UTC)

Merge all the prefix articles[edit]

Should we merge all the articles like mega and giga into this article? They don't contain very much unique information . Most of it is redundant, and we already cover it all in here. They should be redirects with anchor tags going directly to the prefixes' definitions. — Omegatron 22:55, 9 June 2007 (UTC)

Oh. Gerry has a good point. Metric and SI are not the same, but share the same prefixes... — Omegatron 22:56, 9 June 2007 (UTC)
Metric and SI don't totally share the same prefixes. Some prefixes have been ditched by SI (e.g. "myria-"). Jimp 05:19, 4 August 2015 (UTC)

Small section commented out[edit]

"However, even some official prefixes may not be understood by all readers, let alone extrapolations of them, so giving an explanation is advisable when using them in communication (as opposed to using them in notes for oneself)."

This does not seem encyclopaedic. Comments? Rich Farmbrough, 11:00 13 June 2007 (GMT). 11:00, 13 June 2007 (UTC)


I could not find any reference to the supposed prefixes "mancho" (1027) and "mincho" (10-27), so I removed them from the template. — Svenlafe 07:33, 20 June 2007 (UTC)

Requested move2[edit]

From Talk:Peta (prefix)#Requested move2:

Peta (prefix)peta- All prefixes should be moved to prefix- titles, as this is the standard way prefixes themselves are talked about and listed in dictionaries, and so that the (prefix) disambig isn't needed. — Omegatron 02:19, 23 June 2007 (UTC)

Digit grouping[edit]

User:Carlos Porto recently changed some, but not all, of the numbers in the article from using spaces between groups of three digits to using commas to group digits. There are arguments for and against this change:

For comma
The correct kind of space to use would be a non-breaking thin space. I don't know if such a space exists in Unicode, and if it does, I don't know how to enter it into the article. I also don't know how other editors would be able to tell that kind of space had been used.
For space
In those countries where a comma is usually used as a digit separator, it is usually only used to the left of the decimal point, but this article desperately needs a digit separator to the right as well. Since we have to use it to the right, we might just as well use it for everything.

In any case, I don't think it is correct to use a space to the left of the decimal for some numbers, but not for all. Comments? --Gerry Ashton 16:58, 7 July 2007 (UTC)

The argument for commas to the left is the MoS says

Commas are used to break the sequence every three places left of the decimal point; spaces or dots are never used in this role (2,900,000, not 2 900 000).

I'd prefer thin spaces both sides (it's doable, see Template:Delimitnum) but this discussion belongs elsewhere. JIMp talk·cont 05:53, 5 June 2008 (UTC)

Prefix choice[edit]

I don't have any suggestions, but I would have liked to see which is the "correct" way of reporting a length, for example: 450mm, 45cm, 4.5dm, or 0.45m? Is it a matter of taste? Dcaveney 15:44, 31 July 2007 (UTC)

For one thing, put a space between the numbers and the symbol. I don't have a source, but the trend is to only use prefixs where the multiplication or division is by a whole power of 1000. That is, kilo-, mega-, giga- or micro-, nano-, and pico-. Centi-, deka-, deci-, deka, and hecto- are used less and less. The exceptions that I'm aware of are centimeter and decibel.
The situation I could imagine using one of the more unusual prefixes in would be the face of a dial, where using one of these prefixes avoids the use of zeros or decimal points in marking the dial. --Gerry Ashton 18:53, 31 July 2007 (UTC)

The article says: "Prefixes corresponding to an exponent that is divisible by three are often recommended. Hence "100 m" rather than "1 hm" (hectometre) or "10 dam" (decametres). The "non-three" prefixes (hecto-, deca-, deci-, and centi-) are however more commonly used for everyday purposes than in science." Like Dcaveney and the author of the second paragraph in this section, I'd appreciate a reference for the divisible by three factoid. I think it's correct but I don't know its source. I don't think hecto- deca- or deci- are commonly used, here in the UK at least. I believe thay are used in some continental European countries. The centimetre is commonly used in the UK, probably because of the history of the cgs system. The decibel and hectare are also used, though neither would be completely familiar to the man in the street. (talk) 23:19, 15 August 2010 (UTC)

I have a question[edit]

In the article I found the following to be unclear:

Prohibition of multiple prefixes The kilogram is the only SI base unit that has an SI prefix as part of its unit name and symbol. Because multiple prefixes may not be used (such as microkilogram or µkg), the prefixes are used with the unit gram and its symbol g (e.g. milligram or mg).

Could someone please explain the first sentence to me? The rest I follow. If I'm having problems with it, I know someone else must be having problems also. Bad S Mini (talk) 09:24, 29 November 2007 (UTC)Bad S Mini

The sentence just means that the name of the base unit of mass is kilogram and not gram. That makes it different from (say) kilometre, because the base unit of distance is metre. Thunderbird2 (talk) 09:41, 29 November 2007 (UTC)
I have just reworded this. Open4D (talk) 13:21, 20 December 2008 (UTC)

What's Missing?[edit]

10^±0, 10^±1, 10^±2, 10^±3, 10^±6, 10^±9... Where are the SI prefixes for 10^±4, 10^±5, 10^±7, 10^±8, etc? Novjunulo (talk) 23:32, 20 January 2008 (UTC)

No such prefixes exist. Instead, the decimal point should be moved and one of the standard prefixes should be used. For example, if someone wrote 1.403 × 104 m and you wished to use an SI prefix, you would rewrite it as 14.03 km. --Gerry Ashton (talk) 23:40, 20 January 2008 (UTC)
There are obsolete metric prefixes for 10±4. JIMp talk·cont 05:42, 5 June 2008 (UTC)

larger prefixes[edit]

Different sources mention larger prefixes than yotta and smaller ones than yocto, such as [28] where they are called "bogus" prefixes. For example tredo = 10-30. Is there an adoption process for those to become official SI prefixes? I believe to remember that "yotta" was also called a bogus prefix prior to 1991 when it was adopted as an official SI prefix.--Ratzer (talk) 12:06, 6 April 2008 (UTC)

Yes, changes to SI must be approved by the General Conference on Weights and Measures. --Gerry Ashton (talk) 15:18, 6 April 2008 (UTC)
Thank you for the general answer, but I meant it more specific: is there something in the pipeline to adopt more prefixes? When is the next meeting, and is this on the agenda?--Ratzer (talk) 11:01, 7 April 2008 (UTC)


Is xera becoming a pseudostandard for the 1027 prefix?

This mainstream media article mentions xeraflop as a unit of computer performance.

Supercomputer sets record

The Wikipedia article for FLOPS also mentions xeraflop.

Is there a corresponding "small" 10-27 prefix?

What's beyond xera? If the trend continues, I'm guessing the prefix for 1030 will start with W.

--Kreline (talk) 02:59, 9 June 2008 (UTC)

No. All of the 'references' you'll find to the Xera prefix are about the Roadrunner FLOPS record. If you read a few of them you'll notice they're all using the exact same text so there is only a single article that ever used that prefix and it was then regurgitated all over the Web. So where did that article get the prefix? Why, Wikipedia of course! The Roadrunner record coincided with XeraFLOP being incorrectly listed as an SI prefix in the infobox on the FLOPS page. Clearly the original author referenced WP without any fact-checking and of course nobody else copy-pasting the text into their own website/blog/whatever bothered to check either. It's a textbook example of how Wikipedia can spread false information very quickly when people consider it authoritative and nobody checks references. -- ExNihilo (talk) 12:42, 19 June 2008 (UTC)
It has become the default reference and has more Google references than even the Yottaflop, so while it might not be the Queen's English reference, it's most definitely the common parlance. Lordvolton (talk) 23:08, 19 June 2008 (UTC)
Let's not bring your insanity in here aswell. We've been through this (multiple times) on the FLOPS Talk Page. Nothing you're saying makes any sense at all. -- ExNihilo (talk) 00:14, 20 June 2008 (UTC)
LordVoltron, on May 10th, 2006, you added xeraflop to the FLOPS page. Don't deny it., 24th item. — Preceding unsigned comment added by (talk) 21:40, 18 February 2016 (UTC)
Direct link to diff of Lordvolton's addition of xeraflop. --Thnidu (talk) 05:12, 25 April 2017 (UTC)

What about xona, weka, vunda, uda, treda, sorta, rinta, quexa, pepta, ocha, nena, minga and luma?[edit]

This is only one person's idea [29], but surely the scientific community are discussing pay comes after yotta? (although presumably it hasn't yet become SI). Is it worth starting a section on future units (how and when they will be discussed/selected?) Natebailey (talk) 13:06, 22 July 2008 (UTC)

Oops, I see it already exists - :-) Natebailey (talk) 13:09, 22 July 2008 (UTC)
Not anymore, it's been replaced with the joke "hella-" as a possible extension, which is a joke to include this. I think if anything the two should be swapped. Minimally both should be included. (talk) 18:44, 9 February 2012 (UTC)


Why does Exo- redirect here? Because of its resemblance to exa-? It has an entirely unrelated meaning of its own. —Tamfang (talk) 19:09, 15 February 2009 (UTC)

Other and obsolete prefixes[edit]

The cited work by Brewster does mention myria-, but I see no definition for myrio-, nor do I see any mention of symbols for either. --Jc3s5h (talk) 19:08, 16 January 2010 (UTC)

Nike used to support the claim that the prefixes double- and demi- were part of the original metric system. I would like to know more about what kind of source this is. --Jc3s5h (talk) 04:10, 17 January 2010 (UTC)

The source is the French law of 1795 which established the metric system, which I found on The History of the Meter. --Nike (talk) 05:28, 17 January 2010 (UTC)
Do you know if is a personal web site, run by a well-known organization, or run by the government? --Jc3s5h (talk) 05:57, 17 January 2010 (UTC)
I found the site listed as a reference on the French Wikipedia. The translated version is a reference under meter. I don't know the owner. The text is an historical document of the French government, which may be found numerous places. Feel free to replace it with a different link. --Nike (talk) 06:27, 17 January 2010 (UTC)


There has been a bit of a revert war in regards to the "hella" petition. I was of the opinion that it was a bit silly and non-notable, but it seems to have received some attention in the media, including the BBC, so perhaps it should remain in the article. --Nike (talk) 00:17, 11 March 2010 (UTC)

I disagree with including it in the article. The hella petition is not being seriously considered by the BIPM, nor for that matter by any notable scientists, and until it does, it seems a non-notable and trivial topic even if there has been media coverage on it. Not that this is in any way relevant, but given that the student is from the United States, I would have thought his efforts would be more productive in furthering metrication than in creating a new SI prefix. Wcp07 (talk) 06:59, 11 March 2010 (UTC)
I've modified the part about Google "officially implementing" it, to simply "implemented". Google != International Committee for Weights and Measures, and as such, they can't "officially" do anything about it. They do own their own calculator, so they're free to do with that what they wish. It does appear that the student has contacted someone on the committee about this, and that a motion will be introduced. Still, I think most people will agree that the chances of it passing are "hella small". WTF? (talk) 20:32, 7 July 2010 (UTC)
I added in that Google's inclusion is that of an easter egg, not a serious inclusion. As well as reinstated Jim Blower's far more serious and likely proposal. (talk) 19:01, 9 February 2012 (UTC)
Until the BIPM or some other international standards body officially distinguishes between "Easter Eggs" and serious inclusions, I don't think we can use Google's claim that it's an "easter egg" to mean that it isn't serious. Our masters have not yet proclaimed it, so we'd better not mention it in the article, right? WP:RS and all?. :-) Dscotese (talk) 04:41, 23 December 2014 (UTC)
It is definitely in the wrong place at the moment. Perhaps there needs to be a new section entitled New Proposals, in which case Hella (if considered notable - I do not have a view on that) should go there. Dondervogel 2 (talk) 07:37, 23 December 2014 (UTC)
This paraphraph on "unofficial prefixes" seems relevant. Dondervogel 2 (talk) 10:24, 23 December 2014 (UTC)

Is "hella-" the most/only currently notable proposed extension?[edit]

I very much doubt it, but it's the only one mentioned. It's hard to figure out where one would even look for information about proposals for extensions of the system that are under serious consideration. I was trying to remember the prefixes that Greg Egan used in Schild's Ladder, and I was sure this article would at least have a pointer to something helpful—but it doesn't. (I finally remembered that one of them was "vendeka-".) False vacuum (talk) 16:14, 13 August 2010 (UTC)

I found this. It claims nea as 10^27 dea as 10^30 and una as 10^33. It follows the pattern of Greek numbers representing 1000^X where X is the number. We will see what is chosen. I doubt hella will be chosen however.Donhoraldo (talk) 23:49, 28 October 2010 (UTC)
Not at all. This dates back to 2003: (talk) 19:02, 9 February 2012 (UTC)

The footnote of the table[edit]

The footnote to the table says "The metric system was introduced in 1795 with six prefixes." This is not correct. There were eight, myrio- and myria-. They did get dropped in the 60s, but when the metric system was invented, there were still more than the six we retain from that event. (talk) 01:14, 11 December 2010 (UTC)

NPOV statement re kilobits (kb)/kilobytes (KB)[edit]

'In non-standard use, K is often used as a symbol prefix to the units bit and byte to designate the binary prefix kibi = 210 = 1024. Again, try to set an example of encouraging standard usage ('k' for kilo, rather than 'K') in your field or business.'

This, especially the second sentence, clearly fails the NPOV test. In the IT industry a lowercase k means 1000 whereas a capital K means 1024: an important distinction that shouldn't be discouraged (as the above stement clearly does). (talk) 10:38, 13 June 2011 (UTC)

Nem ertem: koczkaknak vagy szamítogepszakiknak: — Preceding unsigned comment added by (talk) 15:50, 23 January 2012 (UTC)
The preceding comment is Hungarian. Google Translate renders it into English as "I do not understand: geeks or computer geeks:". I don't know what the string of digits and dots is supposed to be. --Thnidu (talk) 04:28, 14 August 2016 (UTC)


These prefixes are metric prefixes. Many predate the SI. They are used for non-SI metric units (e.g. "millilitre", "hectare" & "kilocalorie") with the same meaning. Look at the following sentence. "The base unit of length in the cgs system is the centimetre." Is the "centi-" in that sentence an SI prefix? The SI is a metric system; it uses metric prefixes. There are other metric systems; they use the same prefixes. I propose we move the article to Metric prefix. JIMp talk·cont 00:45, 14 February 2012 (UTC)

Moved. JIMp talk·cont 08:04, 5 March 2012 (UTC)
They're defined in SI, even if they're used with other systems - which alone makes them SI prefixes. For that matter, they're used even outside metric, which by the logic above would just make them "unit prefixes". Furthermore, "SI prefix" is by far the most common term for them. I strongly suggest it's moved back to the original name. Kolbasz (talk) 22:52, 21 March 2013 (UTC)

Similar symbols in abbreviations[edit]

I dispute the assertion that "In other financial and business contexts, the letter M is often used to denote multiplication by 1000". A web search will show that the financial and general news media overwhelmingly use m/M, b/B and t/T as abbreviations for million, US billion and US trillion for large quantities, typically currency, population and geological time. Not withstanding the WP deprecation of primary research, my count of 1200 news headlines shows: thousand k = 52% (K = 48%); million m =77% (M = 23%); billion B = 58% (b = 42%); trillion T = 88% (t = 12%). The usage of 'm' is sanctioned in The Australian Government Style Guide (AGPS 2006, p.174), which recommends: "Millions of dollars may be expressed by placing 'm' (unspaced and without a full-stop) after the number (e.g. $2.751m)".

I agree that 'M' and 'MM' are used in U.S. oil industry publications, for oilfield reserves in barrels.

It's neat that the abbreviations M and T for million and trillion match the SI prefix symbols for mega and tera; it'd be even neater if the US oil industry stopped using 2000 year-old Roman numerals, and adopted the 200 year-old metric prefixes, but that's a POV, and not for publication on a WP article.

Adamtester (talk) 04:50, 14 February 2012 (UTC)

Why Yotta is Y and why Yocto is y ?[edit]

This is because the prefix Yotta is a much larger unit than Yocto and the letter Y is bigger than the letter y generated on the computer.

Copyright-- (talk) 19:15, 23 February 2012 (UTC)

Binary prefixes and proposals[edit]

Metric prefixes are decimal. Binary prefixes may have the same names (unless you adhere to the IEC) but they're not metric. Binary prefixes have their own article. They don't need a whole section here.

Likewise the proposed prefixes are not metric in that they've not been adopted into the metric system. JIMp talk·cont 17:29, 2 March 2012 (UTC)

Merged to Unit prefix JIMp talk·cont 08:05, 5 March 2012 (UTC)

Binary prefix[edit]

Does the "binary prefix" mentioned in "Former metric prefixes" mean the same as what the article "binary prefix" talks about? If they are the same, we should make it a wiki link. --Quest for Truth (talk) 04:59, 6 May 2012 (UTC)

It is pushing a point to equate the two. The former metric prefixes were "half" and "double" whereas the binary prefixes are at least 1024. The prefix "half" is still in colloquial use - when in France, I will ask for a "demi-litre carafe vin du maison" (half a litre caraffe of the house wine). Martinvl (talk) 07:00, 6 May 2012 (UTC)
Double and half are not comparable to the metric prefixes. A double-kilogram (or a half-kilogram) is a quantity and a trade measure, but not an acceptable metric unit, as it is inconvenient for arbitrary numbers. For example, 3.14 kilogram is a convenient metric expression, whereas 1.07 double-kilograms and 6.28 half-kilograms are awkward. In the 1795 law half-litre and double-litre were called measures, not units. The purpose of including these quantities in the law was merely to legalize weights and measuring vessels of that size in commerce, not to introduce them as units for science. Nor did the law condone double and half for length measures:
1795 Law, Article 8: Concerning weights and capacity measures, each decimal measure will have its double and its half, to facilitate the trade of products. Thus, there will be the double-litre and the half-litre, the double-hectogramme and the half-hectogramme. .. Article 24: Immediately after the publication of this decree, manufacturing and importing any obsolete measure is forbidden in France and liable to seizure and a fine that is the double of the object's value. [30] Ceinturion (talk) 21:27, 16 August 2016 (UTC)


Why is this unit not included? 10^-10

Angstrom is not a prefix, it's a unit. Jc3s5h (talk) 15:26, 8 May 2012 (UTC)

Move to SI prefix[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.

The result of the move request was: Not moved. Apteva (talk) 15:59, 28 March 2013 (UTC)

Metric prefixSI prefix – The prefixes discussed in this article are defined in SI and are decided upon by CGPM resolutions, and are therefore SI prefixes. That some of the prefixes existed before SI or see use outside SI has no bearing. Kolbasz (talk) 23:26, 21 March 2013 (UTC)

Survey about move[edit]

Feel free to state your position on the renaming proposal by beginning a new line in this section with *'''Support''' or *'''Oppose''', then sign your comment with ~~~~. Since polling is not a substitute for discussion, please explain your reasons, taking into account Wikipedia's policy on article titles.
  • Support: As per my reason in the template, and my comment on the undiscussed move above. The definition of the prefixes are in SI, which makes them SI prefixes by, well, definition. Kolbasz (talk) 23:32, 21 March 2013 (UTC)
  • Oppose:Not all of the prefixes discussed in the article are SI prefixes. We have a whole section on disallowed and obsolete prefixes which never were SI. I don't agree that it has no bearing that some prefixes pre-date the SI nor that they are used outside the SI. The SI is a metric system so any SI prefix is also a metric prefix. Thus metric prefix is a broader term. It's useful to use the broader term in that we can include a discussion on things like myria- which is a metric prefix but not an SI one. It's also useful in that we avoid getting tangled up in the fact that these prefixes are used in all versions of the metric system not just the SI. There are kilocalories, hectares, millibars, microergs, etc.; these are all metric but not SI units. Sure the CGPM decided upon the prefixes but the CGPM has been around longer than the SI. JIMp talk·cont 16:45, 22 March 2013 (UTC)
  • Oppose. Jimp's reasoning is cogent and persuasive. Deor (talk) 17:22, 22 March 2013 (UTC)
  • Oppose for same reasons stated by Jimp. Jc3s5h (talk) 18:01, 22 March 2013 (UTC)
  • Oppose - for the same reason as Jimp. Martinvl (talk) 18:56, 22 March 2013 (UTC)


Any additional comments:
The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

The Greek abbr. "µg," is disfavored as leading to medication errors; the abbreviation mcg is recommended,[edit]

In the metric system, a microgram (µg or mcg) is a unit of mass equal to one millionth (1/1,000,000) of a gram (1 × 10−6), or 1/1000 of a milligram. It is one of the smallest units of mass (or weight) used in a macroscopic context. The symbol "µg" (mu-g) conforms to the International System of Units and is often used in scientific literature, but the United States-based JCAHO recommends that hospitals do not use this symbol in handwritten orders due to the risk that the symbol µ might be misread as the prefix m, resulting in a thousandfold overdose. The abbreviation mcg is recommended instead.[1]

I don't know when this comment was written, but "mc" doesn't seem to be metric prefix for 10−6. Even if it is, it's only used for micrograms and possibly microlitres. — Arthur Rubin (talk) 04:59, 13 February 2015 (UTC)
It is disfavored in medical environments, as the original commentor said. There is no prejudice against it in the IS in general. --Thnidu (talk) 16:27, 19 August 2016 (UTC)


Pronunciation citation[edit]

This sentence doesn't have anything even remotely official backing it up: "When an SI prefix is affixed to a root word, the prefix carries the stress, while the root drops its stress but retains a full vowel in the syllable that is stressed when the root word stands alone."

So, who says this? If it's just a common convention, then why must there be any sort of consistency. One gets the idea that someone just made this up. 08:28, 16 November 2013 (UTC) — Preceding unsigned comment added by (talk)

Possible Volume Incompleteness[edit]

The section on commonly used SI prefixes for volumes only lists millilitres and the like, but somehow does not mention cubic centimetres. Are those really uncommon in English? I am wondering because in German, cubic centimetres are frequently used rather than litre-based units to indicate the size of an empty space inside a vessel, for example in cooking, or for the engine displacement in a car engine. (talk) 14:48, 27 June 2014 (UTC)

I agree. Cubic metres & cubic centimetres are both common enough. Jimp 06:19, 2 July 2014 (UTC)

§ Pronunciation[edit]

The pronunciation section is specific to English:

  • Metric prefix#Pronunciation: The prefix giga is usually pronounced /ˈɡɪɡə/ but sometimes /ˈdʒɪɡə/.
    (That is, usually with the first g "hard", as in game, but sometimes "soft", as in giant.)
  • French: /ʒi.ɡa/
    (Only soft as in géometrie, never hard as in gant.)
  • German: [giga]
    (Hard. German doesn't have a "soft g".)

... and so on.

But nowhere does it say so. Since we're defining an international set of prefixes and everything above this section applies worldwide, we really ought to make it clear that this section applies only to English. And so I'm renaming it "English pronunciation", keeping the old one-word name as an anchor so as not to break any links to it.

To discuss this, please {{Ping}} me. --Thnidu (talk) 04:24, 8 February 2015 (UTC)

@Kbrose: What's your objection, please, to including the three-word phrase "in English as" in a section that discusses prefixes that are used in many different languages, are spelled the same in most or all of them that use the Latin alphabet, but are pronounced in many different ways? Yes, of course this is the English Wikipedia, but few articles deal with such a wide range of cross-linguistic homographous heterophony.
To discuss this, please {{Ping}} me. --Thnidu (talk) 01:12, 15 August 2016 (UTC)
@Kbrose: Eight days, no answer. Reverting. --Thnidu (talk) 21:20, 23 August 2016 (UTC)

Misleading edit[edit]

User:Trackteur has made a misleading edit. Every single prefix in the section formerly named "List of SI prefixes" is an SI prefix. By changing the name of the section to "List of metric or SI prefixes" Trackteur creates the implication that some of the prefixes are not part of SI. Jc3s5h (talk) 12:21, 11 March 2015 (UTC)

Now I think everything is correct. Trackteur (talk) 13:02, 11 March 2015 (UTC)
Tracteur's statement "Now I think everything is correct" appears to have been made without even reading the comment I started this thread with. I cannot convince myself that Trackteur is attempting to engage in meaningful discussion of the issue. Jc3s5h (talk) 13:09, 11 March 2015 (UTC)
Quite so. These edits show no understanding of the relationship between the metric and SI systems, or of the relationship of BIPM to either, and serve only to confuse the reader. NebY (talk) 13:25, 11 March 2015 (UTC)
You've probably noticed that the model [see template] is called Metric prefixes ? Trackteur (talk) 13:31, 11 March 2015 (UTC)
User:Trackteur has made similar edits to many other SI related pages (most of the prefix pages, Centi-, Milli-, etc., for example). These should probably be changed back, but I'm a bit hesitant about reverting so many of one user's edits at once. Suggestions? Rwessel (talk) 21:35, 11 March 2015 (UTC)
I think it's necessary. International System of Units, for example, is part of the system of vital articles and rated as a Good Article. It needs repairing (though I can't do that today). Unfortunately, Trackteur was not only extremely tenacious there, making multiple changes and reverting any corrections whoever made them, but went on to make similar edits on many other articles related to SI or the metric system in general, as if to prove some point. The sheer number of edits in Trackteur's campaign mustn't stand in the way of repairing the damage. Rather, I'd see it as a single corrective action, though spread across many articles and edits. NebY (talk) 22:51, 11 March 2015 (UTC)
Not only does it create the implication that some of these many not be part of the SI, it also creates the impression that the list includes all metric prefixes when it doesn't (e.g. there is no "myria-"). Undo these edits. Jimp 03:45, 12 March 2015 (UTC)

Exa Peta[edit]

In the box in upper right titled "Metric prefixes in everyday use" Peta is given as 10^18. Is that correct? I thought Peta was 10^15 as given in the listing further down. There 10^18 is named Exa. (talk) 19:56, 27 March 2015 (UTC)

You're right; the template {{Common metric prefixes}} was edited recently and an incorrect statement about peta- was added. I removed peta- from that template. Jc3s5h (talk) 20:31, 27 March 2015 (UTC)

6 or 8 original prefixes?[edit]

In section 1. List of SI prefixes The table of prefixes has a note:

The metric system was introduced in 1795 with six metric prefixes. The other dates relate to recognition by a resolution of the General Conference on Weights and Measures (CGPM).

But is "six" right? According to Section 4.1. Obsolete metric prefixes there were 8 prefixes: myria, kilo, hecto, deca, deci, centi, milli, and decimilli, of which the first and the last are obsolete. Benadikt (talk) 21:29, 19 June 2015 (UTC)

I'm pretty sure decimilli was not an original prefix (although it did exist as a semi-common double prefix), rather 10**-4 was "myrio". Anyway, this is a problem in the template producing the infobox (and not a problem here). I've started a discussion at Template_talk:SI_prefixes_(infobox)#Six original prefixes?. It's a somewhat sleepy page, someone bump me if there's no meaningful activity in a week, and I'll make the change. Rwessel (talk) 03:53, 20 June 2015 (UTC)
The french Wikipedia has a similar note, and with Google Translate it says:
The metric system was introduced in 1795 with eight prefixes (two were not kept). The date in the column is that at which the unit was recognized by resolution of the GFCM.
Tre french Wikipedia also has a section about obsolete prefixes (Anciens préfixes), and here 10-4 is called décimilli (dm). It would be interesting to find a reliable source to clarify, if myrio or decimilli was the 10-4 prefix. Benadikt (talk) 18:58, 21 June 2015 (UTC)
Unit_prefix mentions it, but the references are poor. One would think that a scan of the documents from 1795 should be findable online, considering just how significant they are (while those would be a primary source, this would be an acceptable use). It's not hard to find mentions of "myrio" online, but little I'd consider a serious reference. Rwessel (talk) 19:46, 21 June 2015 (UTC)
There is one sourse in the references that cite the original act, The History Of The Metre, section "The 7 April 1795 Act". The act mention myria, kilo, hecto, deca, double, demi, deci, and centi. But neither milli nor myrio/decimilli. However, double prefixes are mentioned with examples like double-hecto and demi-hecto! Benadikt (talk) 10:34, 22 June 2015 (UTC)
I removed myrio. The claim (introduced here: diff) that it was part of the original metric system was unsupported by references. (Not supported by the two references close to that statement: one is a dead link, the other is a footnote in an old encyclopedia which says something else: that Thomas Young would have liked to replace the prefix myria by myrio for linguistic reasons.) Ceinturion (talk) 12:14, 17 September 2015 (UTC)
Given that you are complaining about my edit, you should have pinged me about it.
Regarding the prefix myrio, reading various sources made me believe that myrio was part of the original metric system in the 1790s, but it is also possible that it was established somewhen later in time. However, various sources claim that myrio was used as a decimal prefix to denote 1/10000 somewhen before the advent of SI. For example, myriograd(e) is said to be 1/10000 of a grad(e).
At the same time, we have numerous early 19th century sources in various languages using myrio in the meaning of 10000 (same as myria), as it was proposed by Thomas Young, who was unhappy with some of the French prefixes for linguistic reasons and substituted his own. Given that his alternative prefixes can be found being used in various books around the time, it must have been more a movement than just a proposal, however, I cannot find it being used in much later sources (except for as a reference).
So, it seems myrio was used for both purposes, but perhaps not at the same slot in time or in the same contexts. Since we are obligated to present information from a neutral point of view and not suppress information just because it looks contradictory to us today, we should try to find more and better sources in order to better understand it in the historical context.
--Matthiaspaul (talk) 23:02, 8 October 2015 (UTC)
"Myrio" was pushed by Thomas Young while he was a staunch opponent of the metric system. As a member of a commission for the British Parliament he advised in 1819 against adoption of the metric system in Britain; he championed the twelve based imperial system of units. The purpose of the three nonstandard metric prefixes that he pushed (myrio, chilio, hecato) was more likely to wreak havoc than to improve the metric system. Ceinturion (talk) 22:17, 25 August 2016 (UTC)


Now that this has been added to this article, I suggest that any discussion about the existence or otherwise of the prefix should take place here, instead of at Wikipedia:Redirects for discussion/Log/2016 August 18 where the redirect from Lacta- has been discussed. PamD 20:38, 25 August 2016 (UTC)

@JFG: Thanks for alerting me to Gallica: I've now expanded the mention of "lacta" in this article. PamD 21:12, 25 August 2016 (UTC)
Matthiaspaul, you added a strange prefix 'lacta', and you are specifying it is "obsolete'. You are responsible for that information in wikipedia. Please tell here, on the Talk page, when it was used and when it became obsolete, and please describe the information that your two references provide about Lacta. Ceinturion (talk) 21:32, 25 August 2016 (UTC)

I suggest that this paragraph should be deleted. Currently it starts "It has been asserted...", but even this is not strictly true, in that Cardarelli does not even manage a sentence with "lacta" as the subject. There is just one line in a table:

Prefix Symbol Value
lacta L 105

(Notice the implausible "SI symbol" L, for something not in the SI. )

I searched the Gallica database for:

myriamètre 456 hits
lactamètre zilch
lactomètre milk thing
hebdomètre 1 hit! *
  • Journal télégraphique 1883/04/25 (A15,VOL7,N4) Gallica refers to "Monsieur Clausius" (Clausius?) as proposing the name "hebdomètre" for 1/4 of a meridian. So at least there is evidence for "Hebdometre", but still none for the prefix hebdo-. And even less than none for "lacta-". Imaginatorium (talk) 09:32, 26 August 2016 (UTC)
  • I think that including "lacta-" in a table in a published book is an assertion that it exists, and I reckon the additional material in that paragraph sums up quite nicely the rest of the known information on the prefix - ie two reliable sources which show that it is either extremely obscure or non-existent. PamD 10:42, 26 August 2016 (UTC)
And, for info, OED has nothing for "Hebdo-", and no words starting with "Hebdo" which relate to seventh powers of 10, they're all either about some aspect of the number "seven" or something associated with a week. PamD 10:45, 26 August 2016 (UTC)
Well, yes, I know you worked on the paragraph I'm criticising, and I know you are trying to make fair comments. But my point is that we do not have paragraphs reading: "It has been asserted that a stupping ton is a unit of mass (ref to Cardarelli), but no evidence for this is found in (ref OED etc etc etc). A WP user has pointed out that it's probably a misprint for shipping ton (OR ALERT)". I think my article here establishes beyond doubt that there is a significant amount of total nonsense within the Cardarelli book (whether added by the author, a "translator", or an editor/publisher). I also think it is fairly clear that he really is just making up "symbols", and does not understand that "symbols" are an SI thing, distinct from abbreviations. The French journal I was just looking at from 1883 abbreviates centimetre as "cm." and gramme as "gr."; this, the era when Clausius proposed the "hebdometre" was before the time of "symbols". Since Cardarelli is happy to make up "symbols" for old English units -- randomly, from page 36 we have: "UK wy" for the wey, "UK bu" for bushel, and "UK bk" for bucket -- I do not think inclusion of "L" in a table constitutes evidence of anything from the real world. Imaginatorium (talk) 12:13, 26 August 2016 (UTC)

Copying (slightly edited) the comment I've just made at Wikipedia:Redirects for discussion/Log/2016 August 18, as the two discussions overlap. I have no strong view as to which we should do, but I think it needs to be one or the other:

  • Either

In other words, if "Lacta-" is to be mentioned in this article at all, I think it needs to have the information on its lack of visibility in expected sources. And the redirect and hatnote should exist only if the term "lacta" is mentioned in this article. But I'd be quite happy to see the term removed from this article, and the redirect and hatnote removed. PamD 15:11, 26 August 2016 (UTC)

@Matthiaspaul: Can we slow down slightly? You appear to have decided that a putative "Italian" prefix lacta- and the Indian word lakh are one and the same, going so far as to cite the dreadful Cardarelli book as evidence that the Indian word lakh is abbreviated "L". This is absurd. Can you please start by telling us what it says in the Italian translation of Lange and Forker, please? Imaginatorium (talk) 13:56, 29 August 2016 (UTC)

I wasn't aware that another discussion thread had emerged here. I have already addressed this at Wikipedia:Redirects_for_discussion/Log/2016_August_18#Lacta-. The short answer is: lacta.
In the table "Prefixes for Naming Multiples and Submultiples of Units", Lange's book states "The prefix "myria" is sometimes used for 104 and "lakh" for 105." This applies to both the 9th edition (1956) as well as the 11st edition (1973). The 15th edition (1999) has this table replaced by a list of SI prefixes only. Lange's book dates back to 1934, but I don't know when that sentence was added.
In his answer to my query, Cardarelli explained that he mainly used the Italian translation of the book back in 1970, and that his original notes regarding this prefix were consequently in Italian as well. This is how the Italian lacta- found its way into the book. He has now recognized that this might have caused confusion and will change it to the original lakh- in the next issue of his book.
Your frequent derogatory comments regarding Cardarelli are inappropriate and annoying. The book may contain some errors, but I have experienced the author as being very forthcoming and interested into improving his work. Instead of writing pamphlets trying to publically undermine his integrity you should better have contacted him to make him aware of shortcomings or errors so he can address them in future editions.
--Matthiaspaul (talk) 15:05, 29 August 2016 (UTC)
How did you contact Cardarelli? If possible I will happily contact him and ask for feedback on my analysis of his book. I have repeatedly mentioned that I am not criticising Cardarelli the man, but Cardarelli the book, and I suspect that at least some of the junk (like "1 hat-trick = 1 1/2 pairs", for example) was added by the publisher, probably without his knowledge. But at the same time, the book is a mine of careless scholarship: copying a table of nonexistent Japanese units from a half-century old book without any checking is not exactly best practice. And can you explain: what exactly is this Italian "lacta-" supposed to be?? Imaginatorium (talk) 15:35, 29 August 2016 (UTC)
"How did you contact Cardarelli?"
Via e-mail.
"If possible I will happily contact him and ask for feedback on my analysis of his book."
I think this is a good idea, although perhaps a bit late (but I don't know if he is already aware of your public comments or not - as I sought to establish a fruitful conversation with him I certainly didn't point him at them so far).
"And can you explain: what exactly is this Italian "lacta-" supposed to be?"
As I explained it is the name of the prefix lakh used in the Italian edition of Lange's book.
Consequently I propose to change the redirect lacta- to point to our already existing article on lakh, because now that we know how they are related, this is the better link target.
--Matthiaspaul (talk) 16:12, 29 August 2016 (UTC)
In the other (meanwhile closed) thread, Pam suggested to keep the redirect pointing to here to ensure that the readers will become aware of the issue. That's a good solution, IMHO.
While we still haven't completely solved the puzzle, I think, our collaborative research has brought us a good deal forward in regard to the history and origins of that prefix. I found it quite interesting. Thanks!
--Matthiaspaul (talk) 18:54, 29 August 2016 (UTC)
On my talk page Imaginatorium asked me for a copy of Cardarelli's e-mail, but unfortunetely I can't share that for secrecy of correspondence reasons. I'll try to paraphrase: The scans Cardarelli sent me (and which I could share) were from the English version of Lange's book stating in a table about "Prefixes for Naming Multiples and Submultiples of Units": "The prefix "myria" is sometimes used for 104 and "lakh" for 105". Cardarelli explained that he was mostly using the Italian version of the book [31] back then, which, according to him, was using the term lacta instead. His original notes on this subject were in Italian as well, and this is how the term found its way into the book decades later. Cardarelli said that he still owns a copy of the Italian version of the book as well, but that it is located in a (personal) library/archive in Europe, so that he has no immediate access to it (as he lives in Canada now). Hope it helps. --Matthiaspaul (talk) 07:40, 31 August 2016 (UTC)

Once again, I suggest that the non-existent prefix, and mention of lakh (part of the Indian numbering system, not a prefix) should be removed. The only "source" for the prefix lacta- which we have is the mention in Cardarelli's book; now that this author says that this was a "mistake for lakh", all justitication has gone. Equally, the claim that "lakh" is a prefix is only supported by a one-line note in a book first published in 1934. This is not credible evidence, especially given the copious information about how this is actually used at Indian numbering system and lakh. I have written a section in my Cardarelli critique: Hebdo- and lacta-. Imaginatorium (talk) 16:01, 31 August 2016 (UTC)

I support Imaginatorium's suggestion, and PamD's concurring "I'd be quite happy to see the term removed from this article, and the redirect and hatnote removed". This supposed prefix has no more reality than a typo. --Thnidu (talk) 17:02, 31 August 2016 (UTC)

Half and double not "symmetrical"?[edit]

The section Obsolete metric prefixes now* ends with the claim: "The halving and doubling prefixes were dropped because they were neither decimal nor symmetrical." What does the last word, "symmetrical" refer to? These are certainly not "decimal", but 2 and 0.5 are each other's reciprocal, so I don't see how they could be more symmetrical? Can anyone explain? (* I just removed the 'lacta' paragraph.) Imaginatorium (talk) 04:48, 2 September 2016 (UTC)

Thanks. The original text seems to have been added by an IP on 17 January 2010 and it looks as if it never had a source. See Special:Contributions/ if you want to examine some of their other edits. I recommend removing the text as unclear and unsourced. Johnuniq (talk) 05:30, 2 September 2016 (UTC)
@Johnuniq and Imaginatorium: Done. Good analysis and research, compadres. --Thnidu (talk) 06:02, 2 September 2016 (UTC)

Possible reforms[edit]

I know I've heard of proposals to change k, h, and da to K, H, and D. Or to change k to K while doing away with h, da, d, and c. Does anyone else remember coming across such? Should there be a section about this? --Khajidha (talk) 16:22, 7 December 2016 (UTC)

There is no such proposal. It would be falling back into the 19th century. See the section about D and H at this talk-page. Ceinturion (talk) 20:01, 7 December 2016 (UTC)
No, I've read these SOMEWHERE. They specifically stated that the proposal was to align with the rest of the prefix system where capitals were used for positive exponents and lowercase for negative ones with prefixes only being utilized for every third power of 10. These patterns for the rest of the system did not exist in the 19th century. Maybe it was just one particular author who thought up this idea but didn't get any organized support.--Khajidha (talk) 20:39, 7 December 2016 (UTC)

More Metric Prefixes[edit]

Hello. I'm anonymous. Because I have to be. If you absolutely need a clue who I am, I'm...You know what? I'll just say I'm from Scratch. Speaking of Scratch, here's a project I did that has these prefixes: This isn't about me anyway. I just wanted to make a very extended list of prefixes. Please tell me if any are wrong. I made quite a lot of them up based on other things I know about the prefixes.

NOTICE: I KNOW they've come from geometry and co. I just wanted to get them all up here in the list. It kind of makes sense though, since the polysystem and the metric system have interlocking numbers (like hecto for 100).

Here's the list...

[Commented out. See below. --Thnidu (talk) 07:40, 9 January 2017 (UTC)]

WAHEY!!! That's a LOT, isn't it?

Here are some links that helped me (half of them talk about shapes): (OK, I admit I just put that link there to show which ones I knew in the first place.) (You can see that there are some of these metric prefixes replaced with "on" in the cells.) (You people helped!) (That's where I got all the unknown Googol numbers from. In the Murderous Maths book "Savage Shapes", there is a "Googlagon". I actually got confused by that book as to whether a 100-sided polygon is "Centagon (10^-2)" or "Hectogon (10^2)".) (There's Brontobyte and Geopbyte...What. The Heck!?) (There's Bronto and Omega.)

If you've read the whole thing, THANK YOU!!! You may actually help me know!

Bye peoples! (talk) 19:28, 30 December 2016 (UTC)

These aren't metric system prefixes, (some of ) these are numeric prefixes used in organic chemistry and geometry. The metric prefixes are ONLY the ones already listed in this article. They are the only ones used with metric units to produce larger or smaller units.--Khajidha (talk) 18:11, 3 January 2017 (UTC)
* Glad you're having fun,, but none of this has anything useful to do with this article or talk page. I'm commenting most of it out and bolding your statement of origin.--Thnidu (talk) 07:47, 5 January 2017 (UTC) (talk) 21:38, 8 January 2017 (UTC)

Dear Editor who dare not speak his or her name (talk):
Allow me to direct your attention to Wikipedia's Talk page guidelines, which begin as follows (emphasis added):

Talk pages are for improving the encyclopedia, not for expressing personal opinions on a subject or an editor..
The purpose of an article's talk page (accessible via the talk or discussion tab) is to provide space for editors to discuss changes to its associated article or project page. Article talk pages should not be used by editors as platforms for their personal views on a subject.

Your own made-up list is not a potential contribution to the article: other contributions with a much better claim to notability have been rejected as not part of the metric system. (I crossed out my own words there because your list has no claim to notability at all.)

You have freely admitted that many of these, besides your own inventions, are not part of the metric system. To quote you:

NOTICE: I KNOW they've come from geometry and co. I just wanted to get them all up here in the list.

Go put your list on your own blog, or on some MIT play page; it's very much in that spirit. Maybe you can post it in the Infinite Corridor. Here, though, it's just a waste of space, especially with the blank lines you've just inserted. As a (possibly excessive) courtesy to you, instead of deleting it I'm commenting it out for a while to give you the opportunity to copy and save it for yourself. (Even that isn't necessary, as you could always get it off the history page, but I'm not sure you know your way around here well enough to do that, as indicated in part by your insistence on blank lines instead of using a bulleted list.) Kindly do not prove your trollishness beyond dispute or defense by messing this page up again. --Thnidu (talk) 07:40, 9 January 2017 (UTC)

Is the letter "s" in use of an SI prefix?[edit]

The article said that letters such as S and T had to be skipped because they were already symbols of units. The s also got skipped in septo- because s was in use of a prefix at the time? I checked and so far none of the SI prefixes have the letter s as their symbol. Could someone explain why they put that down? Thanks (talk) 17:36, 16 April 2017 (UTC)

Double? Demi?[edit]

Weights for scales.JPG

What do those prefixes mean, it said they mean 2 and 1/2. But they don't have symbols, and they don't even represent powers of 10. Could someone tell me about them please? I know almost nothing about them. Thanks. (talk) 20:54, 24 April 2017 (UTC)

I assume a demimetre is 0.5 m and a doublemetre is 2 m. What more is there to know? I don't see why they would need to be powers of 10. Dondervogel 2 (talk) 21:57, 24 April 2017 (UTC)
Double and demi were added to the French law to allow shops to use a weight box like the one in the photo, and the law allowed the name "double-hectogram" for 200 gram, and "half-hectogram" for 50 gram. Double and half were convenient for trade and commerce, but useless for science: they are used for measures and weights, but not for units. They were legal, but not metric (not decimal). I think the choice of this wikipedia article to apply the name "metric prefix" to the words "double" and "half" is unusual and confusing. Ceinturion (talk) 23:35, 24 April 2017 (UTC)
I think the paragraph "Obsolete metric prefixes" is absolutely fine. These were part of the original French system (so of course "demi" is the French for "half", and "double", pronounced /du:bl/, is the French for "double"), and since we call the original French system "metric" they were indeed "metric", though they were not "decimal". They have a lot more right in an article on "metric prefixes" than the computer science use of "K" to mean 2^10, it seems to me. Imaginatorium (talk) 03:06, 25 April 2017 (UTC)
Demi and double are two ordinary French count nouns, and count nouns should not be called metric prefixes (milli up to kilo). Demi and double turn a unit into a quantity: a demi-hectogramme is not a metric unit, as writing "6.28 demi-hectogrammes" would interfere with the simple math of the metric system. When translating from French to the language of another early metric country, like Dutch, demi and double were translated as the ordinary count nouns, just like when translating to English (see example at the right, from the year 1871, [32]). The French law from 1795 does not identify demi and double as prefixes for units; instead it specifies that shops are allowed to use weights (that is: objects, not units) such as a half and a double hectogram. Ceinturion (talk) 23:53, 26 April 2017 (UTC)
I see your point; though "count noun" is not really the right term, I think. And to niggle, 'demi' attaches to what is already a quantity, since un demikilo de fromage is just half as much cheese as un kilo de fromage (spelling? sorry). I spent some time struggling to get rid of the "not symmetric" claim; I would not really mind if these were removed completely. But then someone would keep putting them back, worse. Imaginatorium (talk) 05:11, 28 April 2017 (UTC)

So a doublemeter is 2 meters and a demimeter is 5 dm. Right? (talk) 22:21, 25 April 2017 (UTC)

Yes, except that demi-metre is French, which translates in English as half meter. Ceinturion (talk) 23:53, 26 April 2017 (UTC)

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What if ...[edit]

in small prefixes, changing the "first letter" coping with the great ones: micro/Mega, gano/Giga, tico/Tera, pento/Peta, etto/Exa, zepto/Zeta, yocto/Yota, nefto?/Nova, decto/Desa? {milli --> lepto --> kepto/Kila }
Tabascofernandez (talk) 00:52, 15 July 2017 (UTC)

Where is Power?[edit]

I came to this article to verify abbreviation of kilowatt as kW. There is no section referencing the Watt and it's prefixes. I think 'Power' and the Watt needs to be added as an entry in Section 2.1 as it is not a minority entity and is in daily use. Andrew ranfurly (talk) 12:13, 21 October 2017 (UTC)

that would be found here (talk) 22:44, 11 September 2018 (UTC)

The Energy section talks about the non-metric unit 'Calorie' but never mentions the SI unit 'Joule'[edit]

If this article is about Metric prefixes but the Energy section discusses the non-metric unit 'Calorie' and never mention the SI unit of energy the Joule Andrew ranfurly (talk) 12:20, 21 October 2017 (UTC)

'deka' again[edit]

I find it curious that the standard US English spelling 'deka' of the prefix is not even mentioned in the article ... —Quondum 13:16, 3 April 2019 (UTC)