Talk:Parts-per notation

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2003-2004 discussion[edit]

"The ppm value is equivalent to the absolute fractional amount multiplied by one million." This needs to be expanded. For those who actually need this article, this will be more confusing than the words "parts per million."

An example would help (I mean, an example like "a drop of blood in a 50 gallon drum would be about n parts per million"). --Larry Sanger

Is the exact calculation/definition:

ppm = solute / solvent * 1000000 ?


ppm = solute / total solution * 1000000 ?

or could be both ? like we use percentage, sometimes it needs to specify which two we are comparing ?

also, is it must be the same units ? like mass over mass,

or it could be mass over volume, without specifying other variables like temperature ?

Article structure[edit]

All of the information here is equally applicable to ppt, ppb, ppq etc and to some extent duplicates what is included in the concentration article. I therefore propose we move some of the content from the concentration page here and redirect to this from all uses of ppt etc. The articles are currently a bit of a mess with duplicate stubs, a redirect to the concentration and complete lack of consistency.

Just to summarise what pages I think should be redirected here:

This has been changed to a disambiguation page. PAR 15:44, 1 January 2006 (UTC)

--NHSavage 08:38, 14 August 2005 (UTC)

Yes, the mentioned pp- stubs should be redirected to a parts per notation page with a good explanation. Duplication of the relevant material in concentration rather than a move of that info would be in order. Vsmith 13:58, 14 August 2005 (UTC)
This article has been renamed after the result of a move request. Please now continue with the cleanup. violet/riga (t) 13:48, 21 August 2005 (UTC)
Cleanup done. I think that this article still needs some work to further explain the differences between part per by volume, mass etc. I will think some more about this and also link to this from the concentration article. --NHSavage 20:47, 26 August 2005 (UTC)


The examples don't seem to be too accurate. A drop is usually defined as 0.05 ml, which then gives;

1 drop in 50 ml = 1‰, 50ml is a very small cup
1 drop in 50 l = 1ppm 50 l is about 11 gallons, not 40
1 drop in 50 cubic metres = 1 ppb
1 drop = 1ppt, a 50 m swimming pool is 50*25*2 = 2,500 m^3
1 drop in 50,000,000 cubic metres = 1ppq, 50,000,000 m^3 is equivalent to a lake covering a square kilometre, and 50 metres deep, which is more than "medium sized" IMHO --Tom k&e 11:23, 6 September 2005 (UTC)

  • I’ve addressed this in the re-write. Thanks. Greg L (my talk) 20:41, 4 December 2007 (UTC)

Other uses[edit]

PPM is also used to describe the accuracy of precision equipment such as a voltage calibrator. For example, see . 23:53, 19 April 2006 (UTC)

Thank you for this, I have added it in to the article.--NHSavage 06:50, 20 April 2006 (UTC)

absolutely confusing[edit]

Do you mean “parts per” notation, perhaps? Jclerman 15:35, 24 June 2006 (UTC)


The notes need to be totally redone. 3 does not refer to anything about it, and there is no 4. --Storkk 01:20, 20 August 2006 (UTC)

  • The notes section was disjointed and not the proper, Wikipedia way of doing things. After the re-write, its contents were either 1) redundant, 2) tangential, or 3) incorrect. Accordingly, the entire section has been deleted. Thanks. Greg L (my talk) 20:43, 4 December 2007 (UTC)

What the...[edit]

Well thsi article stinks. Its bloody confusing. If parts per hundred is the same as 100% stuff, then that means number of molecules per hundred total, not per every other 99. So 1pph is 1 molecule per 100 total molecules.

Just say that!Tourskin 03:41, 12 February 2007 (UTC)

I am concerned about the definitions as well. For example, it is not accurate to define "parts per hundred" as one particle for every 99 other particles. Instead, that might be a fair definition of "one part per hundred." But the definition is not helpful if the reader seeks to understand what "10 parts per hundred" means. Does that mean "10 particles for every 99 other particles"? Not at all; it means "10 particles for every 90 other particles." Nissynis 14:38, 8 June 2007 (UTC)

  • Agreed, the “1 part versus 99 parts remaining” was unnecessarily confusing. As now revised, the article is consistently 1 part per 100 (etc) parts examined. Thanks. Greg L (my talk) 20:44, 4 December 2007 (UTC)


This article is complete crap - sorry for the terminology, but if my old chemistyr teacher was here to see this awful article... Parts per million is NOT involving particles. It involves mass. So for NaCl which could be 5pp09 (UTC)

Wikilinks to billion, a disambiguation page[edit]

In order to avoid having this article link to the disambiguation page billion, I'm going to change the links to go to billion (word) which redirects to long and short scales, where there is a decent discussion of the ambiguity of the word billion. --AndrewHowse (talk) 14:17, 28 May 2008 (UTC)

  • Fabulous. Greg L (talk) 20:31, 28 May 2008 (UTC)
  • On second thought, the end effect was, in one case, have a sentence that had two links to long and short scales. I think it’s better to avoid the temptation to link for the sake of linking. Granted, million had a link in the sentence, but that makes sense, since “million” can go to only one article. Greg L (talk) 05:51, 20 June 2008 (UTC)

ppm vs. ppmv[edit]

In environmental chemistry we make a distinction between parts per million {or billion, etc.} by *volume* vs. ppm by *weight*. For a dilute solution, such as NaCl in water, concentration is often expressed as weight of solute divided by mass of solution (typically assuming 1 g/mL for dilute water-based solutions) -- i.e., ppm by weight. Mass/volume notation such as micrograms/mL is also used for liquid solutions.

Low concentrations of pollutant gases in air are often expressed in units of ppm or ppb by volume (ppmv and ppbv). Volume-based units refer to the partial volume of the trace gas in the total volume of air. Assuming the ideal gas law, parts by volume is equivalent to parts by molecule count as described in the article.

The concepts of "parts by weight" vs. "parts by volume" need to be sorted out clearly, particularly since "ppmv" redirects to this article, even though this term is not mentioned in the text. Comments? Jamesf991 (talk) 02:22, 20 October 2008 (UTC) jamesf991

  • Jamesf991: Parts per million (volume) is just one of very many measures. As the article’s table clearly shows, it can be parts per million voltage. The article does indeed use many mass-per-mass examples, since that is by far the most common measure in science. However, all lead sections in the article make it clear that parts-per measurements can be any measure, such as this statement: “The expression “1 ppm” means a given property exists at a relative proportion of one part per million parts examined.”

    You make a good point with regard to how volume-per-volume measurements are linking to this article. Note that the really accurate, scientific measure for gases is moles-per-mole, not volume-per-volume, such as the BIPM’s 2004 measurement of 9.332 mmol/mol for argon (S Y Park, J S Kim, J B Lee, M B Esler, R S Davis and R I Wielgosz). Nevertheless, articles linking volume-per-volume measurements could be better served. So I’ve added some vol-per-vol and mole-per-mole examples. Greg L (talk) 21:04, 28 November 2008 (UTC)

Ppmv redirects here but there is no mention of ppmv. Should we have the "NOTATIONS FOR DIMENSIONLESS QUANTITIES" mention ppmv? Or does that not make sense? ~a (usertalkcontribs) 23:17, 30 November 2009 (UTC)

Yes there should be an example of ppmv, which is really by mole as long as the ideal gas law holds. For example, measuring 380 ppm CO2 in air is the equivalent of 380 molecules CO2 per 1,000,000 molecules of air. All atmospheric measurements of gases are reported with this ppmv convention and are known as mixing ratio, to distinguish from concentration, which is typically mol / volume or molecules / cc. I can't figure out how to edit the article though. —Preceding unsigned comment added by (talk) 19:07, 11 April 2011 (UTC)

The Olympic Swimming Pool example[edit]

Genty & Deflandre (1998) measured the volume of drops of water falling from stalactites, they found that a drop of water is 0.14 ml (not 0.05 ml) irrespective of drip rate etc. So 1 ppt is 56th of a drop of water dispersed throughout an Olympic sized swimming pool. --Diamonddavej (talk) 17:24, 10 December 2008 (UTC)

It's a really bad example to have in the lead given that it's fractional drops per pool. Also, given the ambiguity of billion and trillion, I think the best example would use parts per million. I haven't come up with anything with a snappy picture yet... Vagary (talk) 18:16, 4 August 2009 (UTC)

Volume ppm & ppb[edit]

After taking analytical chemistry, I went back to this page and realized the ppm (stated as µL/L) is wrong (µL/L is ppb). I changed it to ppb, and added a ppm line. Savonnn (talk) 02:26, 29 January 2009 (UTC)

Moles/moles or grams/grams?[edit]

I came to this page in search of answers to the question of whether "25 ppb" of lead ions in a pond refers to moles per totals moles or grams lead over total mass of solution. I did not find that answer. After reading the talk page, I am given the impression that ppb commonly refers to mass measurements, but can refer to a molecule or mole ratio. Correct?

I think this should be explicitly stated on the page. I'm not adding it myself because I'm still not positive it's correct.

Furthermore, it says that units don't matter, because the ratio will be the same, which is false and misleading - 25 molecules of lead for every billion of solution is clearly not the same as 25 grams of lead in a 1 billion gram solution of lead and water. Thanks. Ana The Person (talk) 22:48, 14 April 2009 (UTC)

I absolutely agree. I also came to this article trying to reconcile whether ppm referred a mol ratio or a mass ratio. Yes, the units should always cancel, but the number is still dependent on the unit used. Personally, I feel the entire expression is ambiguous. If I had enough confidence to editg wikipedia articles, I'd add it myself. Someone who has a better feel for what's appropriate please add a section discussing this! Hovissimo (talk) 00:20, 29 January 2011 (UTC)

Use not improper[edit]

This addition of an example for "improper use" is not improper according to the description in that paragraph, because it divides mass by mass. I will therefore remove it. It may be unusual for other reasons, though. If that is so, I wouldn't object to it being added with its own referenced explanation. But unless that is important, I would rather leave it out since it can be confusing. — Sebastian 00:05, 24 February 2010 (UTC)

Formula needs to be updated[edit]

i don't know how to do it, i just noticed it. down the bottom of the page there is an old style formula, perhaps it could be converted? just trying to help. —Preceding unsigned comment added by (talk) 10:21, 21 April 2010 (UTC)

 Done Thanks for pointing it out! Physchim62 (talk) 12:03, 21 April 2010 (UTC)

Concentration vs Fraction[edit]

There is a difference between fractions and concentrations, see IUPAC Green book, page 41: RolfSander (talk) 16:06, 3 March 2011 (UTC)

I was not able to find any relevant information on page 41. However, Pages 77 and 78 contain a discussion of ppm. Q Science (talk) 20:52, 11 March 2011 (UTC)
On the Keeling curve, the Scripps Institution of Oceanography reports the CO2 concentration in ppm. As a result, that is the standard way all atmospheric gas concentrations are reported. IMHO, any attempt to change to another "standard" is just minor players trying to control the world class research centers. Q Science (talk) 21:10, 11 March 2011 (UTC)
I think several replies are necessary to your comment: 1) Was it your intention to call me a "minor player"? Are you maybe overreacting because those "climate sceptics" drive you crazy? 2) I don't deny that many scientists from world class research centers report "concentrations in ppm". That doesn't change the fact that it is wrong. Try this: Make two plots of vertical ozone profiles. One showing concentration (1/cm3), one showing mole fraction (ppb). Do you see the difference? RolfSander (talk) 21:24, 11 March 2011 (UTC)
Sorry, I was considering the SI standards board to be the "minor player". Part tongue in cheek, and part not. There are many industries where the major players and the standards boards don't agree. (Microsoft comes to mind.) Either the standards are ignored or, eventually, they are changed. Claiming that some usage is "wrong" won't convince scientists to change their standard.
Ozone is interesting since it is normally reported in Dobson units. Q Science (talk) 23:34, 11 March 2011 (UTC)


I would like to delete the section "Air measurements". The suitability has nothing to do with the parts-per notation. It is a question of mass fraction vs mole fraction. The gasoline part is difficult to understand and probably wrong. The conversion at the end of the section should go to the mass concentration page, it is not specific to air measurements. The rest of the Convertibility section could be moved into the overview, I don't think it is important enough to have its own section. Any objections? RolfSander (talk) 02:57, 10 March 2011 (UTC)


First it is said that: “the language-dependent terms ‘part per million,’ ‘part per billion,’ and ‘part per trillion’…are not acceptable for use with the SI to express the values of quantities.”[7]

Then in the table below all "not acceptable" trems are highlighted in green. PPM is in black. How is PPM language dependant? I can see how PPB and PPT are "language-depenent" (really short/long scale dependant). I work for a high precission pscilator company, we use ppm notation all the time... — Preceding unsigned comment added by (talk) 13:22, 9 November 2011 (UTC)

Indeed, PPM is not language-dependent. However, it still should not be used because of the mass fraction vs mole fraction (or volume fraction) problem. I removed the confusing part of the NIST quotation and replaced it with an ellipsis.RolfSander (talk) 14:28, 9 November 2011 (UTC)
And I changed the "highlighting" color in that table to red (actually darkred to better blend in) because it was confusing to use green for something, that should better be avoided. --Matthiaspaul (talk) 08:02, 15 August 2017 (UTC)

another important ppm[edit]

Can we please include this important ppm and the two most common EC(electrical conductivity)to ppm "conversion factors" - the sodium chloride (NaCl)ppm500 scale and the potassium chloride (KCl)ppm700 scale solutions. These two ppm scales and the confusion around them should be an article in itself. Including this information will help a lot of people. thanks. — Preceding unsigned comment added by (talk) 17:40, 10 February 2012 (UTC)

Talk about confusing...[edit]

Reading the article and the comments here, I must agree with the "unit purists". Part and particle have the same etymologic base, so to me it would seem logical that ppm talks about particles, like atoms or molecules. Now it seems that that is very very wrong, at least according to Tourskin, it's mg per kg. So now I'm wondering, when the maximum allowed quantity of let's say lead in drinking water is given in ppm, is that actually mg/liter they mean??
And the comment of Greg L on how to make a 30% solution reminds me why chemistry somehow seemed less of a science to me than physics. I arrived here from Nickel tetracarbonyl, inhaling a concentration of 30ppm would be immediately fatal to humans, but now I'm not so sure if this still means what I think it means, since mg/kg would make it a few times more deadly...

But the article Concentration makes everything clear... Let me just quote the relevant sections:

  • However, the deprecated parts-per notation is often used to describe small mole fractions.
  • However, the deprecated parts-per notation is often used to describe small mole ratios.
  • However, the deprecated parts-per notation is often used to describe small mass fractions.
  • However, the deprecated parts-per notation is often used to describe small mass ratios.
AAAAAAahhhhh!!! (╯°□°)╯︵ ┻━┻ ... (talk) 21:07, 8 March 2012 (UTC)

Practical vs Theoretical Issue.[edit]

There is a problem with this article that pervades it from start to finish. That problem is the cognitive dissonance between what some authors want the world to be like and the reality. The reality is that parts per - is NOT consistently or mostly unitless. There are ample examples in this article where various units are mixed, yet the thrust of the article is to ignore the numerous "exceptions" to a flawed definition. I argue that it is NOT in Wikipedia's to PRESCRIBE use, rather is should DESCRIBE use. The article does a very poor job of explaining that different ratios are used in different contexts. I think that this article is necessary, and should not be replaced with a "disambiguation" page, but I think the article should be much clearer about the many alternative uses of the term. For instance, it is just not simply true that the reason that drinking water uses mg/l is to make it easier for the public. It was (and I believe still is) a common practice in analytical (wet) chemistry to work with analytes on a volumetric basis but measure results on a weight basis, the natural result (especially in trace analysis) is mg/L, which I can tell you since I lived it was the basis for early EPA regulatory Methods. It would be great IF everybody agreed that parts per - will only apply to unitless ratios, but that's just not the way it is. This article needs a more universal DESCRIPTIVE perspective. I suggest that a table of common parts per - uses be created, along with citations to the literature showing each use, as well as perhaps (if possible) the discipline it is found in (eg. sanitary engineering, pollution control, machining, analytical chemistry, electrochemistry, nuclear chemistry, etc. etc.) I am willing to cede the point, although a rigorous article would have quantified the claim, that mass/mass is the most common ratio found as parts per -. It is probably the plurality usage, I have serious doubts that it is the majority usage. (talk) 07:20, 21 August 2013 (UTC)

NMR subsection[edit]

Expanded NMR section slightly and made it its own subsection. This use of parts-per notation is different than some others because it gives a quantity that doesn't depend on the instrument used. It makes it the only practical way to discuss chemical shifts. It's meant to be a subsection so for references and more detailed information readers can go to the linked articles. I didn't mention coupling constants (which don't depend on field strength and aren't given in ppm) -- the idea is to show that parts-per is useful in removing a variable from certain measurements. Roches (talk) 13:05, 22 February 2014 (UTC)


I'm confused. mppcf means "Millions of particles per cubic foot of air". Why should this be the same as "0.1 mg/m3 respirable dust as designated by OSHA" ??? Besides, "mppcf" is a concentration (mass/volume) and not a parts-per notation (dimensionless fraction) RolfSander (talk) 09:55, 28 November 2015 (UTC)

I concur with the concerns raised by RolfSander above, and have removed the addition of mppcf. - Ryk72 'c.s.n.s.' 21:58, 28 November 2015 (UTC)


Should the unit "uno" be pluralized (2 centiunos, 2 milliunos and so on), as per the regular SI rules? It also seems that the reference to that IUPAP proposal is dead. Is it now? — Mikhail Ryazanov (talk) 20:00, 7 February 2016 (UTC)

Fixed the link, thanks. --Matthiaspaul (talk) 17:43, 15 August 2017 (UTC)