Wikipedia:Manual of Style/Dates and numbers

This Manual of Style, like all style guides, attempts to encourage consistency and ease of reading. The guidelines here are just that: guidelines are not inflexible rules; one way is often as good as another, but if everyone does it the same way, Wikipedia will be easier to read, write and edit.

New contributors are reminded that clear, informative and unbiased writing is always more important than presentation and formatting. Wikipedians are not required to follow any of these rules. (See the joy of wiki editing.)

Dates

Years, decades, and centuries

See Anno Domini for a discussion on what is meant by AD and BC notation, and Common Era for a discussion on what is meant by CE and BCE notation.

A page title that is just a positive whole number is always a year. Pages also exist for days of the year, decades, centuries and even millennia. The formats for references to years are:

• 474
  • [[474]]
• 474 BC (note no periods) or 474 BCE
  • [[474 BC]] or [[474 BCE]]
• 18th century (note that century is not capitalized, and "1700s" is not a century, but a decade, as illustrated below.)
  • [[18th century]]
• 10th century BC or 10th century BCE
  • [[10th century BC]] or [[10th century BCE]]
• 1830s (note no apostrophe)
  • [[1830s]]
• December 1983 (note that December is not linked)
  • December [[1983]]
• 320s BC or 320s BCE
  • [[320s BC]] or [[320s BCE]]

Articles for the year 500 BC and earlier should be redirected to the relevant decade. Articles for the year 1700 BC and earlier should be redirected to the relevant century. Articles for the year 4000 BC and earlier should be redirected to the relevant millennium.

Note that the 1st century BC was from 100 BC–1 BC (there was no year 0) so 1700 BC would be the first year of the 17th century BC, 1800 BC would be the first year of the 18th century BC, etc. Similarly, 4000 BC was the first year of the fourth millennium BC, not the last year of the fifth millennium BC.

When only an approximate date is available the abbreviation "c." (circa) may be used; see the example at Rameses III below. When a date is uncertain—because the sources are unreliable—that fact should be noted and, if possible, the source specified. For example, "according to Livy, the Roman Republic was founded in 509 BC", or "The Mahabharata is traditionally said to have been composed in 1316 BCE".

Date formatting

Adding square brackets "[[DATE]]" to full dates allows date preferences to work. Editors are not required to link full dates, but most full dates in Wikipedia are linked so that each user's date-formatting preference appears in the text. For this to work, at least the day and the month must be included; some date preferences won't work unless a year is also linked. For example:

• Month and day
  • [[February 17]] → February 17
  • [[17 February]] → 17 February

• Day and month and year
  • [[February 17]], [[1958]] → February 17, 1958
  • [[17 February]] [[1958]] → 17 February 1958
  • [[1958]]-[[02-17]] → 1958-02-17
  • [[1958-02-17]] → 1958-02-17

Avoid overlinking dates

If the date does not contain a day and a month, date preferences will not work, and square brackets will not respond to your readers' auto-formatting preferences. So unless there is a special relevance of the date link, there is no need to link it. This is an important point: simple months, years, decades and centuries should only be linked if there is a strong reason for doing so. See Wikipedia:Make_only_links_relevant_to_the_context for the reasons that it's usually undesirable to insert low-value chronological links; see also Wikipedia:Manual of Style (links)#Internal links.

Usage of links for date preferences

Examples where date preferences do not work:

• year only. So [[1974]] → 1974. Generally, do not link, unless they will clearly help the reader to understand the topic.
• month only. So [[April]] → April. Generally, do not link.
• century. So [[20th century]] → 20th century. Generally, do not link.
• decade. So [[1970s]] → 1970s. Generally, do not link (including an apostrophe (1970's) is incorrect).
• year and month. So [[April]] [[1974]] →April 1974 Generally, do not link.
• day of the week (with or without other date elements). So [[Tuesday]] →Tuesday. Generally, do not link.

An unlinked date, such as "February 17, 1958" will not be converted. To create a date that is linked but not converted, use a "piped" link with alternate text, for example "[[February 17|17 February]]".

Using the date formatting feature in section headers complicates section linking, see date formatting.

Dates in article titles

In article titles, dates will not be converted. It is usually preferable to use the format preferred in the variety of English that is closest to the topic. For topics concerning Europe, Australia, Oceania and Africa, the formatting is usually 17 February 1958 (no comma and no "th"). In the United States and Canada, February 17, 1958, (with two commas—the year in this format is a parenthetical phrase) is correct; in Canada, 17 February 1958 is common.

ISO date formats

The ISO formats, e.g., 2004-02-17 and 2004-FEB-17 are less widely comprehended. Redirects for other ISO forms should always be created. The YYYY-MM-DD format currently only follows the style of ISO 8601, but not the proleptic Gregorian calendar.

Incorrect date formats

• Do not use numbers to express a month, except in full ISO 8601 format, which always includes the year. Always express a month as a whole word (for example, "February") to avoid ambiguity. In the ISO 8601 format, a leading zero is always added to single-digit months and days.
• Do not use two digits to express a year unless at the end of a range, e.g., "1970-87" (the same for BC). In all other cases, use four digits for years and decades after AD 999 (the same for BC). Using the less formal two-digit form for a decade is acceptable when not ambiguous; for example, when referring to the decade of the 20th century known as "the eighties", use "1980s" or, less often, "the '80s", not just "80s".

• Use consistent date formatting throughout an article, unless there's a good reason to vary it.

• Do not use ordinal suffixes:
  • Incorrect: "February 14th" and "14th February"
  • Correct: "February 14" and "14 February"

• Do not use articles:
  • Incorrect: "the 14th of February"
  • Correct: "14 February"

• Do not put a comma or the word "of" between a month and year:
  • Incorrect: "December, 1945" and "December of 1945"
  • Correct: "December 1945"

An important exception to these guidelines is that direct quotations—the word-for-word reproduction of a written or oral text—should not be altered to conform to the Wikipedia "Manual of Style". In other words, a paragraph such as the (fictional) quotation from a newspaper report is fine as is:

"Tony Blair, responding to critics in his party, said 'The world has totally changed since the 11th of September.' He was echoing earlier sentiments by Lord Ronald McDonald, who said that 'nine-eleven' was the day that the American public woke up to the reality of terrorism."

Dates of birth and death

• Charles Darwin (12 February 1809–19 April 1882) or (12 February 1809 – 19 April 1882) or (12 February 1809 - 19 April 1882)
  • Locations should be included in the biography portion of the body article. For example, "(February 12, 1809 in Shrewsbury, Shropshire, England – April 19, 1882 in Downe, Kent, England)" should be separated to "(February 12, 1809–April 19, 1882) ... He was born in Shrewsbury, Shropshire, England ... He died in Downe, Kent, England".
• Socrates (470 BC–399 BC) or (470 BC – 399 BC) or (470 BC - 399 BC)
  • When only the years are known.
• Serena Williams (born September 26, 1981)
  • For a person still living at the time the article was written.
  • Notice that the form is NOT "(September 26, 1981–)"
• Offa (died 26 July 796)
  • When the date of birth is unknown.
• Genghis Khan (c. 1162–August 18, 1227) or (c. 1162 – August 18, 1227)
  • When the date of birth is known approximately.
• Dionysius Exiguus (c. 470–c. 540) or (c. 470 – c. 540)
  • When dates of birth and death are known approximately.
• Robert Menli Lyon (born 1789, date of death unknown)
  • When the date of death is unknown, but the person is certainly now dead.
• Rameses III (reigned c. 1180 BCE–c. 1150 BCE) or (reigned c. 1180 BCE – c. 1150 BCE)
  • When only the dates of the reign are known and only approximately.

Note the use of "c." rather than "circa", "ca." or a question mark.

Ranges of dates are given with a spaced or unspaced hyphen or en dash (–). See Wikipedia:Manual of Style (dashes).

Eras

Both the BCE/CE era names and the BC/AD era names are acceptable, but be consistent within an article. Normally you should use plain numbers for years in the Common Era, but when events span the start of the Common Era, use AD or CE for the date at the end of the range (note that AD precedes the date and CE follows it). For example, [[1 BC]]–[[1|AD 1]] or [[1 BCE]]–[[1|1 CE]].

In articles about prehistory, if you use BP (before present) or MYA (million years ago), expand these abbreviations when you first use them, as most readers will be unfamiliar with them.

Different calendars

You can give dates in any appropriate calendar, as long as you also give the date in either the Julian or Gregorian calendar, as described below. For example, an article on the early history of Islam may give dates in both the Islamic calendar and the Julian calendar.

• Current events should be given in the Gregorian calendar.
• Dates before the adoption of the Gregorian calendar on 1582-10-15 must be given in the Julian calendar and not converted.
• Dates of events in countries using the Gregorian calendar should be given in the Gregorian calendar. This includes much of Europe from 1582, the British Empire from 1752-09-14, Russia from 1918-02-14, and so on (see the Gregorian calendar article).

Other dates are ambiguous. Your options for this period are:

• Give the dates in the Julian calendar only. This means that the dates will match the dates in the primary sources for that period. If you do this you should indicate that the dates are in the Julian calendar.
• Convert the dates to the Gregorian calendar. This means that events in different countries can be correlated.
• Give dates in both calendars, for example, William Shakespeare died on 1616-04-23 (Old Style)/1616-05-03 (New Style).

At some places and times, dates other than 1 January were used as the start of the year. The most commonly encountered convention is the Annunciation Style used in Britain and its colonies in which the year started on 25 March. See the New Year article for a list of other styles. You should always convert dates so that they correspond with years starting on 1 January. If it is important to preserve consistency with primary sources, you may give the date in the original style, but then you must also give the date in the modern style. For example, Elizabeth I of England died on 1602-03-24 (Old Style)/1603-04-03 (New Style).

Times

Time formatting

Context will determine whether the 12-hour or 24-hour clock should be used.

Times in the 12-hour clock should use colons, and lower case "a.m." or "p.m.". These suffixes generally cannot be omitted, except that "12 noon" and "12 midnight" should be used instead of "12 a.m." and "12 p.m."; some readers find the latter ambiguous.

24-hour clock times follow the same format, except without the a.m./p.m. suffixes. Discretion may be used to determine if leading zeroes should be used. 00:00 refers to midnight; 12:00 refers to noon.

Examples:

12-hour clock	Not	24-hour clock	Not
2 p.m.	2pm	14:00	14.00
2:34 p.m.	2.34 PM	14:34	1434
12:04:38 a.m.	12.04 38″ A.M.	00:04:38 or 0:04:38
12 noon	12:00 p.m.	12:00

Time zones

When writing a date, first consider where the event happened and use the time zone there. For example, the date of the Attack on Pearl Harbor should be December 7, 1941 (Hawaii time/date). If it is difficult to judge where, consider what is significant. For example, if some cracker in Japan hacked the Pentagon, use the time zone for the Pentagon.

If you know it, include the UTC date and time of the event in the article, indicating that it's UTC.

Numbers

Numbers

Very large numbers may be divided up by commas every three places, starting from the decimal separator in both directions. (Note that this is different from SI/ISO 31-0 notation where a thin space is used every three places.) In scientific contexts, scientific notation is preferred. Additionally, large round numbers can generally be assumed to be approximations; it is not necessary to always qualify with "approximately" or some similar term.

A period (".") must be used as the decimal point, separating the integer part from the fractional part.

For numbers between minus one and plus one, include the leading 0 ("0.02", not ".02").

The minus sign has two representations. One is the normal hyphen-minus ("-") available on every computer keyboard (twice on such with numeric keypad); the other ("−") is easiest entered as −.

Percentages

The format of the numeric and percentage terms should match. Thus pair 7 with % and seven with percent or per cent.

Numbers in words

Numbers may be written as words or numerals, although note that many users prefer that numbers less than ten be spelt out. It is considered awkward for a numeral to be the first word of a sentence: either recast the sentence or spell the number out. A consistent approach is required within each article.

Fractions standing alone should be spelt out unless in a percentage. If fractions are mixed with whole numbers, use numerals.

Billion is understood as 10⁹ in the United States, Canada and most of the English-speaking world. However, in most Germanic and Romance languages, it means 10¹². See the detailed discussion in English-language numerals, long and short scales.

Natural number

Natural number has two meanings:

• positive integer, or
• non-negative integer (including zero).

When referring to such numbers, explicitly use one of the above phrases rather than "natural numbers", unless it does not matter which interpretation is chosen.

Ranges

Sometimes numbers and dates are expressed in ranges, such as "4–7" for the numbers 4 through 7. It is often preferable to write this out (for example, "4 to 7" or "four through seven") to avoid confusion with "four minus seven".

See Wikipedia:Manual of Style (dashes) for more information.

Non-base-ten numbers

For numbers in bases other than base ten,

• in computer-related articles, use the C programming language prefixes, that is, 0x for hexadecimal, 0 for octal and 0b for binary. It may be a good idea to include a note at the top of the page about these prefixes.
• in all other articles, use subscript notation, for example 137₉, 241₆, 2X9₁₂, A87D₁₆ (use _and)
• For bases eleven and higher, use whatever symbols are convention for that base. Where applicable, use uppercase rather than lowercase letters, thus 0x5AB3 not 0x5ab3. Preferred digits are A—F for ten to fifteen.

Measurements

Units

Wikipedia articles are intended for people anywhere in the world. Try to make articles simple to read and translate.

• Conversions should generally not be removed.
• If editors cannot agree about the sequence of units, put the source value first and the converted value second.
• Spell out source units in text. Use digits and unit symbols for converted values and for measurements in tables. For example, "a pipe 100 millimetres (4 in) in diameter and 10 miles (16 km) long".
• Converted values should use a similar level of precision as the source value. For example, "the Moon is 380,000 kilometres (240,000 mi) from Earth", not "(236,121 mi)".
• Use standard abbreviations when using symbols. For example, metre is m, kilogram is kg, inch is in (not " or ″), foot is ft (not ' or ′).
• Do not append an s for plurals of unit abbreviations. For example, kg, in, yd, lb not kgs, ins, yds, lbs.
• Some non-metric units have more than one version. Be specific. For example, U.S. gallon or imperial gallon rather than just gallon. Similarly, use nautical mile or statute mile rather than just mile in aviation, space, sea and in some other contexts.
• The reader should see a space between the value and the unit symbol, for example "25 kg" not "25kg". Use   for the space (25 kg) to ensure that it does not break lines.

Binary unit prefixes

Multiple-byte units
Decimal Value Metric 1000 kB kilobyte 10002 MB megabyte 10003 GB gigabyte 10004 TB terabyte 10005 PB petabyte 10006 EB exabyte 10007 ZB zettabyte 10008 YB yottabyte 10009 RB ronnabyte 100010 QB quettabyte	Binary Value IEC Memory 1024 KiB kibibyte KB kilobyte 10242 MiB mebibyte MB megabyte 10243 GiB gibibyte GB gigabyte 10244 TiB tebibyte TB terabyte 10245 PiB pebibyte – 10246 EiB exbibyte – 10247 ZiB zebibyte – 10248 YiB yobibyte – 10249 – – 102410 – –
Orders of magnitude of data

In computing, binary prefixes can be used to quantify large numbers where powers of two are more useful than powers of ten. They are commonly written and pronounced identically to the SI prefixes, but each successive prefix is multiplied by 1024 (2¹⁰) rather than 1000 (10³).

Using the prefixes kilo-, mega-, giga-, etc., and their symbols K, M, G, etc., in the binary sense can cause serious confusion. In January 1999, the International Electrotechnical Commission introduced in IEC 60027 the prefixes kibi-, mebi-, gibi-, etc., and the symbols Ki, Mi, Gi, etc. to specify binary multiples of a quantity. They have since been officially adopted by many other organizations.

• Prefixes for binary multiples - NIST
• When is a kilobyte a kibibyte? And an MB an MiB? - IEC

The use of the new binary prefix standards in the Wikipedia is not required, but is recommended for use in all articles where binary capacities are used. In articles where the precise byte capacities are important to description, the binary prefix should be used with binary capacities and the SI prefix should be used with decimal capacities (and should be noted as decimal if not immediately clear). If a contributor changes an article's usage from kilo- etc. to kibi- etc. where the units are in fact binary, that change should be accepted. However, because they are less familiar, binary unit prefixes such as MiB should be linked to avoid confusion. Link as [[Mebibyte|MiB]] to avoid a disambiguation page.

Do not change all SI prefixes to IEC prefixes in computing contexts, only those that are actually being used in a binary sense. For example, do not change a "160 GB HDD" to "158.69 GiB" (still less "160 GiB"), but you can change 512 MB RAM to 512 MiB RAM where it is important to do so. (Notice that the number does not change because the SI prefix was used in a binary sense. Both usages are acceptable, but the MiB reference is less ambiguous.)

Measures that typically use decimal multiples:

• Capacities of hard disk drives and some storage media
• Network and bus speeds

Measures that typically use binary multiples:

• Memory and cache sizes
• Some storage media

Examples

• The highest score recorded for the Deuces High pinball game was 11,933,750.
• The hippopotamus stands 1.5 metres (5 ft) at the shoulders and weighs between 2,700 and 4,500 kilograms (6,000–9,900 lb).
  • The [[hippopotamus]] stands [[1 E0 m|1.5 metres]] (5 ft) at the shoulders and weighs between [[Orders of magnitude (mass)|2,700 and 4,500 kilograms]] (6,000-9,900 lb).
• ... between 2.7 and 4.5 tons.
• The first sub-four-minute mile was run by Roger Bannister.
• The 155-millimetre diameter projectile offers a wide range of options for battlefield usage.
• 10² = 100
  • 10² = 100
• A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234×10²⁹, and a small number such as 0.0000000000234 can be written as 2.34×10⁻¹¹.
  • A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234×10²⁹, and a small number such as 0.0000000000234 can be written as 2.34×10^−11.
• The computer has a 160 GB HDD and 512 MiB of RAM.

See orders of magnitude and the talk page there for ongoing, possibly resolved debate on which style of exponent notation to use for large numbers.

Geographical coordinates

Geographical coordinates on Earth should be entered using a template. This standardizes the format. It also provides a link to a page with several links to maps of the coordinates, and is part of a new way to handle geographic information in Wikipedia.

Depending on the form of the coordinates, three template formats are available. For just degrees, use d mode:

{{coor d|DD|N/S|DD|E/W|}}

For degrees/minutes, use dm mode:

{{coor dm|DD|MM|N/S|DD|MM|E/W|}}

For degrees/minutes/seconds, use dms mode:

{{coor dms|DD|MM|SS|N/S|DD|MM|SS|E/W|}}

Where:

• DD, MM, SS are the degrees, minutes, seconds listed one by one
• N/S is either N or S, depending on which hemisphere
• E/W is either E or W, depending on which hemisphere

Examples

For the city of Oslo, located at 59° 55′ N, 10° 44′ E, enter:

{{coor dm|59|55|N|10|44|E|}}

which becomes 59°55′N 10°44′E

For a country, like Botswana, the d mode is more appropriate:

{{coor d|22|S|24|E|}}

Which becomes 22°S 24°E

For higher accuracy, use the dms mode:

{{coor dms|33|56|24|N|118|24|00|W|}}

Which becomes 33°56′24″N 118°24′00″W

Examples of articles using geographical coordinates:

• Airports: London Heathrow Airport
• Cities: Amsterdam
• Islands: Jan Mayen
• Mountains: Mount Baker

Decimal degrees, minutes, or seconds

• degrees can be specified with decimals, in d mode
• minutes can be specified with decimals, in dm mode
• seconds can be specified with decimals, in dms mode

Example:

{{coor d|12.0433|S|77.0283|W|}}

Which becomes 12.0433°S 77.0283°W / -12.0433; -77.0283

Attributes

The final field, following the E/W, is available for specification of attributes, such as type, region and scale. For more information, see the geographical coordinates WikiProject.

Note

Due to planned enhancements in functionality, the above template concept is subject to change. As long as the above templates are adhered to, any necessary changes will be performed automatically by a robot.

Currency

In country specific articles such as Economy of Australia use only the symbol specific to the country, in this case $, with an italicized note placed at the top of the article to make this clear.

In articles which are not country specific, such as Wealth, use ''[[United States dollar|US$]]100'' or ''one hundred [[United States dollars]]''. Use the most commonly used English abbreviation, and only link to the relevant article at the first usage. If there is no common English abbreviation or symbol, use the ISO 4217 standards.

Conversions

Conversions can be made into other currencies which are more familiar to most readers such as the Euro or United States Dollar. Conversions should be in parenthesis after the original currency, with the year given as a rough point of reference, for example, one thousand Swiss francs (approx. US$763, c.2005), rounding to the nearest whole unit. Currency converters can be found at xe.com or FXConverter by searching the web.

Examples

Good style

• NZ$100,000
• AU$100,000
• US$100 million
• 2000 Chinese renminbi
• Two thousand Chinese renminbi

Bad style

• $190 — This can lead to ambiguity in non-country specific articles as to which dollar is meant.
• $100 — this is hard to read
• 100$ — Although it is read like this, it is not a standard way to write it. Canadian Dollars are expressed this way when written in Quebec. This is also the way Portuguese Escudos were expressed prior to the Euro being introduced.
• $200 (US)
• $US200