Wikipedia:Manual of Style/Dates and numbers

This Manual of Style has the simple purpose of making things look alike — it is a style guide. The following rules do not claim to be the last word. One way is often as good as another, but if everyone does it the same way, Wikipedia will be easier to read and easier to use, not to mention easier to write and easier to edit.

New contributors are reminded that clear, informative and unbiased writing is always more important than presentation and formatting. Writers are not expected or required to follow all or any these rules: the joy of wiki editing is that perfection is not required.

Dates

Years, decades, and centuries

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 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 4th millennium BC, not the last year of the 5th 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 of unreliable sources that should also be noted, ideally with a reference to the source. 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

The addition of square brackets '[[' and ']]' to some dates permits date preferences to work. Editors are not required to add square brackets but some readers welcome it. Date preferences only work if the date includes a day and a month. For example:

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

• Day Month 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

If the date does not contain a day and a month, then date preferences do not work. In such cases, square brackets around dates do not respond to user preferences. So unless there is a special relevance of the date link, there is no need to link it. Examples where date preferences do not work are:

• year only. Such as 1974
• month only. Such as April
• century. Such as 20th century
• decade. Such as 1970s
• year and month. Such as April 1974

An unlinked date such as "February 11, 1958" will not be converted. To create a date that is linked but not converted, use a link with alternate text, for example "[[February 17|17 February]]".

Note that using the date formatting feature in section headers complicates section linking, see date formatting.

In article titles dates will not be converted. It is generally preferable to use the format used by local English speakers at the location of the event. For events within Europe, Oceania and Africa, that is usually 11 February 2004 (no comma). In the United States and Canada, February 11, 2004 (with comma) is correct. Redirects for the other common forms should always be created.

Note that the YYYY-MM-DD format currently only follows the style of ISO 8601, but not the proleptic Gregorian calendar.

Incorrect date formats

What not to do:

• 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. Please note that in the ISO 8601 format, a leading zero is always added to single-digit months and days.
• Do not link two digits to express a year unless discussing the years from AD 10 to AD 99 (the same for BC). Wikipedia deals with all of history, not just the last hundred years, so always use four digits for years and decades after AD 999 (the same for BC). Using the less formal two-digit form for a decade within an article is acceptable when it does not create an ambiguity. For example, when referring to the decade of the 20th century known as the eighties, use [[1980s]] or [[1980s|'80s]], not just [[80s]].
• Do not use ordinal suffixes:
  • Incorrect: February 14th
  • Correct: February 14
  • Incorrect: 14th February
  • Correct: 14 February
• In general, avoid using multiple date formats in the same article.
• Do not put a comma or the word of between a month and year:
  • Incorrect: December, 1945
  • Incorrect: December of 1945
  • Correct: December 1945

Note, however, the content of a direct quotation — the word-for-word reproduction of a written or oral utterance — should not be altered to conform to the Wikipedia "Manual of Style". In other words, a paragraph like the (fictional) one below is fine:

• Tony Blair, responding to critics within 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)
• Socrates (470–399 BC) or (470 – 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.
• Rameses III (reigned c. 1180–c. 1150 BCE) or (reigned c. 1180 – 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

There is a proposal to amend this section on Wikipedia:Eras/Compromise proposal. Please discuss the proposal on its talk page and cast your votes on the voting page.

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 Annunication 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

Times should be written in the 24-hour clock (hh:mm or hh:mm:ss). The 12-hour clock has a number of problems: it isn't used throughout the world; it often makes it harder to convert between different time zones; and "12:00 am" and "12:00 pm" are ambiguous. When using 12-hour times anyway, it is important that they are identified with an am or pm designation, so that they are not mistaken for 24-hour times. Be sure to use the same time format consistently throughout an article and do not edit articles merely to change the time format.

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 acceptable representations. One is the normal hyphen-minus ("-") available on every computer keyboard (twice on such with numeric keypad), the other, typographically favorable one ("−") is easiest entered as −.

Percentages

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

Numbers in words

Numbers may be written as words or numerals. Editors should use a consistent guideline throughout an article. A number should not appear in both forms in the body (excluding tables and figures) of the same article. However, it is considered awkward for a numeral to be the first word of a sentence: either recast the sentence or spell the number out.

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

In different English dialects, billion may be 10⁹, as in the U.S., or 10¹², as was traditional in Britain. Try to avoid these names altogether and instead use scientific notation, or at the very least explain your usage at its first occurrence in an article. The same problem arises with other numbers in the -illion family beyond the millions. See 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. Use an en dash for these when possible. 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.

Measurements

Units

The issue of whether all units should be metric (SI) is being debated at Wikipedia:Measurements Debate, but they are always acceptable.

• In scientific contexts, such as physics and chemistry, use SI units exclusively, but
• if in a field a quantity is always given in one form, there is usually no need to perform a conversion. Link to the article explaining the unit, though. For example, atmospheric ozone concentration is measured in Dobson units.
• The exact value and unit from the most reliable or, if applicable, normative source should always be retained, e.g. traffic speed limits in the UK and USA are in "mph", elsewhere "km/h", and "knots" in aquanautics, but nowhere "m/s". To avoid conversion edits that result in lesser accuracy, such instances should be made obvious.
• Unless there is a historical or other reason to use one style over another, editors may choose whether to use metric, U.S. customary units, or Imperial units primarily. It may be helpful to readers to offer equivalents, but this should not be done if it reduces the flow of a sentence or otherwise interferes with the quality of the writing.
• If equivalents are given, these should be to the same level of precision as the original measurement and in parentheses, for example, "the Moon is 400,000 km (250,000 miles) from Earth", not "(248,548.477 miles)".
• Metric equivalents should be given for historical or unusual units, where these are appropriate. Multiple equivalents, i.e. metric and U.S. or imperial, are cumbersome and shall be avoided.

In-text written-out units are preferred ("two metres" instead of "2 m"); otherwise use standard abbreviations or symbols for metric units—m for metre, kg for kilogram, etc. (see SI for the list)—and two-letter abbreviations for inch-pound units—in for inch (not " or ″), ft for foot (not ' or ′), yd for yard, mi for mile, lb for pound, gal for gallon, pt for pint, qt for quart, and so forth. Never append a plural s to abbreviations (no "kgs", "yds", "kts", or "lbs"). Where possible, use the symbols with unit combinations, for example use ft/s rather than fps.

The terms fluid ounce, pint, quart, gallon, barrel, and ton are ambiguous units, so they must be specified more precisely. You may assume that ounces and pounds are Avoirdupois unless otherwise indicated. When the unit is part of a quote, and is within quotation marks, it should not be changed, though a conversion may be added in brackets after the quote, if it is an unusual unit.

Areas of land should be given in square kilometres, km², which can be entered as km². This form is preferable to km², which can add extra leading. When describing areas of agriculture, forests, parks, wilderness, etc., hectares (ha) are an acceptable (not mandatory) alternative to square kilometres. Smaller areas use m² etc.

Volumes should be given in cubic metres (m³) or litres (l or L), where it is common usage.

Note that the compact superscript style works well with areas and volumes (i.e. ² and ³), but where zero, four to nine or minus are required, one should resort to <sup>.

Larger masses may be given in tons (t) and for approximations it is often not necessary to disambiguate between the metric ton (sometimes "tonne") and the English tons, because they are quite similar in size.

In general, all SI prefixes are acceptable, but an editor may choose to use a subset thereof.

The reader should see a space between the value and the unit symbol: "25 kg", not "25kg". To ensure that the value and the unit symbol are displayed on the same line, editors should use a non-breaking space character rather than a standard space: type 25&nbsp;kg rather than 25 kg. Avoid entering the character directly, even when possible, for some browsers substitute all instances of it with the normal, breaking space.

Measurements (both number and unit together) of dimensions with existing orders of magnitude pages should be linked to the appropriate page.

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 — — —
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 to "Mebibyte", since MiB links to 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 m (5 ft) at the shoulders and weighs between 2,700 and 4,500 kg (6,000–9,900 lb).
  • The [[hippopotamus]] stands [[1 E0 m|1.5&nbsp;m]] (5&nbsp;ft) at the shoulders and weighs between [[Orders of magnitude (mass)|2,700 and 4,500&nbsp;kg]] (6,000&ndash;9,900&nbsp;lb).
• … between 2.7 and 4.5 tons.
• The first sub-four-minute mile was run by Roger Bannister.
• The 155 mm diameter projectile offers a wide range of options for battlefield usage.
• 10² = 100
  • 10&sup2; = 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&times;10²⁹, and a small number such as 0.0000000000234 can be written as 2.34&times;10^&minus;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 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.