Wikipedia:Manual of Style/Dates and numbers/sandbox

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, the 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 of these rules: the joy of wiki editing is that perfection is not required. Copy-editing Wikipedians will be referring to these pages and pages will be gradually made to conform with this guide.

In an international encyclopedia, date and number styles in particular have the ability to confuse. For example, someone used to dealing in miles, gallons and pounds may be completely unfamiliar with kilometres, litres and kilograms, and vice versa. Many people are likely to be unfamiliar with technical or academic jargon. The general philosophy behind these rules is that date and number styles should be chosen so as to be readily understandable to as many people as possible. Remember, you are writing for the reader, not for yourself! So use styles that as many people as possible are likely to use and understand themselves. Where this guide is silent on an issue, bear the general philosophy in mind and you are unlikely to go wrong.

Dates and times

Years, decades, centuries

A page title that is just a number is always a year. Pages also exist for days of the year, decades, centuries and millennia. The Wikipedia standard formats for references to years are as follows (note in particular the punctuation style and where capital letters are used):

474
- [[474]]
474 BC
- [[474 BC]]
18th century (Note also that "1700s" is not a century, but a decade as illustrated below.)
- [[18th century]]
10th century BC
- [[10th century BC]]
1830s
- [[1830s]]
December 1983
- December [[1983]]
320s BC
- [[320s BC]]

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 abbrieviation "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 BC."

Eras

The Wikipedia standard is to use BC/AD, and not the BCE/CE notation used by many academics. This is because far more people understand and use the BC/AD notation than the BCE/CE notation, and is in line with the general philosophy outlined above.

The exception to this rule is that Wikipedia custom has built up that articles relating to Buddhism always use the BCE/CE notation, and that articles relating to Judaism use either the BC/AD or BCE/CE notation, but are internally consistent in their choice of style.

Where only very approximate dates are known, it may be better to use alternative, more vivid ways to describe dates. For instance, instead of referring to something that happened around the year 3000 BC, it may be better to describe it as happening 5,000 years ago.

Only use BC or AD with a year when it is necessary to disambiguate the year - this usually happens when describing events of or spanning the first centuries BC and AD, and the first time a BC date is mentioned in an article.

Note that BC, BCE and CE follow the number of the year, but AD precedes it:

For example, [[1 BC]]–[[1|AD 1]] or [[1 BCE]]–[[1|1 CE]].

In articles about prehistory, do not use BP (before present) or MYA (million years ago) without explaining to the reader what they mean. Often it will be best to avoid using this terminology completely.

Dates

Dates should always be wikified so that each reader sees the dates formatted according to their own preference. As numbers dropped into articles can be momentarily jarring, the link also has the benefit of highlighting to the reader that you are talking about a year. You should use one of the following formats, and use that format consistently throughout an article:

Month Day, Year:

[[February 17]]

[[February 17]], [[1958]]

Day Month Year:

[[17 February]]

[[17 February]] [[1958]]

YYYY-MM-DD (an ISO 8601 format):

[[1958]]-[[02-17]]

Importantly, if a date is to be understood by the software, it must be "wikified", as shown above. An unlinked date such as "February 11, 1958" will not be converted. To create a date which 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 outside North America that is usually 11 February 2004 (no comma). In North America it is usually February 11, 2004 (with comma). Redirects for the other common forms should always be created.

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 (eg "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. Wikipedia deals with all of history, not just the last hundred years, so always use four digits for years and decades after AD 999. 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 piped links to "years in music" or analogous pages (eg [[1983 in music|1983]]). (See Wikipedia:Wikiproject Music standards for discussion).
In general, avoid using multiple date formats in the same article.

Note, however, that the content of a direct quotation — i.e., 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)
Socrates (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.
Offa (died 26 July 796)
- When the date of birth is unknown.
Genghis Khan (c. 1162 – August 18, 1227)
- When the date of birth is known approximately.
Dionysius Exiguus (c. 470–c. 540)
- When dates of birth and death are known approximately.
Rameses III (reigned c. 1180–c. 1150 BC)
- When only the dates of the reign are known and only approximately.

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

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 15 October 1582 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 14 September 1752, Russia from 14 February 1918, 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 23 April 1616 (Old Style)/3 May 1616 (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 24 March 1602 (Old Style)/3 April 1603 (New Style).

Times

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. Never use "12:00 am" or "12:00 pm" as they are ambiguous.

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.

Time zones can cause confusion. For example, Japanese troops started to move across the frontier of the New Territories of Hong Kong at dawn on December 8 1941 [1] . The attack on Pearl Harbor was at 07:53 Hawaiian time which was 03:23 December 8 Japan Standard Time (see The Pearl Harbor Strike Force, Note). Hong Kong Time is one hour behind Japanese Standard Time so the attack on Hong Kong was part of a theater wide near simultaneous coordinated attack and was not 24 hours later as the timing at first glance seems to imply. Another example is anniversary of the end of World War II in Europe which is celebrated as May 8 in Britain and the USA but on the 9 May in Russia because when hostilities ceased at 23:01 hours Zulu time it was already May 9 in the Soviet Union. So if you know it, and it is relevant, also include the UTC date and time of the event in the article, indicating that it's UTC.

Style for numbers, weights, and measures

Very large numbers, such as pinball scores, should be divided up by commas every three places. (Note that this is different from SI notation where a thin space is used every three places.) In scientific contexts, scientific notation is preferred: see below.

A dot "." should be used as the decimal point, separating the integer part from the fractional part.

The issue of whether all units should be metric (SI), Imperial, or American units is being debated at Wikipedia:Measurements Debate. These points are mostly non-controversial:

In scientific contexts, such as physics and chemistry, use SI units. Unless for any historic reference or other particular reason, it is not necessary to state American or Imperial units in parentheses.
If using American or Imperial units, give the metric equivalent as a courtesy.
If using metric units, remember that many readers will not know what you mean and will be aided by the equivalent in American or Imperial units.
Equivalents should be given to the same level of precision as the original measurement, for example, "the moon is 250,000 miles (400,000 km) from Earth", not "402,336 km".
If the quantity is always given in one form, you need not perform any conversion at all. For example, atmospheric ozone concentration is measured in Dobson units; there is no need to give a metric equivalent, but do link to the article on the unit once.

In text written out units are preferred ("two metres" instead of "2 m"), otherwise use standard abbreviations or symbols for metric units without an added s in the plural — m for metre, kg for kilogram, etc. (see SI for the list) — and two-letter abbreviations for inch-pound units — in for inch (not "), ft for foot (not '), yd for yard (not yds), mi for mile, lb for pound (not lbs), gal for gallon, pt for pint, qt for quart, and so forth. 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, eg as being either US or Imperial/British. By wikilinking gallon, pint, etc., you allow the reader unfamiliar with the term to find out what it means. For example an American may not understand a reference to a UK gallon, but as long as gallon is linked, can easily find out. You may assume that ounces and pounds are Avoirdupois unless otherwise indicated.

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

Speed should be given in m/s by default, but in km/h, or mph when this is conventional (speed limits, etc.).

Areas of land should be given in km², which can be entered as km². This form is preferable to km2, which adds extra leading in some browsers. Smaller areas in m² etc. Volumes in m³, cm³ etc. Note that the compact superscript style works only for 1, 2 and 3 (unless you use numeric Unicode codes &8304; for superscript zero and &8308; to &8313; for superscript 4 to 9). This means that the  style has to be used when general superscripts are required, as in the examples below.

When describing areas of agriculture, forests, parks, wilderness, etc., hectares are an acceptable (not mandatory) alternative to square kilometres.

The reader should see a space between the value and the unit symbol: "25 kg" and 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 kg rather than 25 kg.

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 (425–710 st or 6,000–9,900 lb).
- The [[hippopotamus]] stands [[1 E0 m|1.5 m]] (5 ft) at the shoulders and weighs between [[Orders of magnitude (mass)|2,700 and 4,500 kg]] (425–710 st or 6,000–9,900 lb).
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
- 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.

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.

Number names

In a non-technical context, and with the exception of displaying tabulated data, the words per cent (or percent if you're using American English) should be written out in full, rather than using the % symbol.
Whole numbers between zero and ten should be written out in full. Numbers higher than ten may be represented by numerals, except where they appear as the first word in a sentence, in which case they should be written out in full.

Natural number

Natural number has two meanings:

positive integer
non-negative integer (i.e. including zero)

Except where it does not matter which is chosen, explicitly use one of the above instead of natural numbers.

In Wikipedia, "natural number" unequivocally means "non-negative integer", as the natural number article explains. So if you link to the natural number article, it's clear what you mean.

Ranges

Sometimes numbers and dates are expressed in ranges, such as "4–7" for the numbers 4 to 7. Use an en dash for these when possible. See Wikipedia:Manual of Style (dashes) for more information.