Editing 12-hour clock (section)

{{Short description|Time counting system}}
{{Redirect|AM and PM|other uses|AM PM (disambiguation)}}
{{Redirect|Ante meridiem|text=For the meridian 180° both east and west of the prime meridian in a geographical coordinate system, see [[180th meridian|antimeridian]]}}
{{Use American English|date=January 2021}}
{{Use dmy dates|date=November 2017}}

The '''12-hour clock''' is a time convention in which the 24&nbsp;hours of the day are divided into two periods: '''a.m.''' (from [[Latin]] '''{{Langx|la|ante meridiem|label=none}}''', translating to "before midday") and '''p.m.''' (from Latin '''{{Langx|la|post meridiem|label=none}}''', translating to "after midday").<ref name="EncyclopaediaBritannica">{{cite encyclopedia | title =Time | encyclopedia =The New Encyclopædia Britannica | volume =28 | pages =660 2a | year= 1986 }}<br />{{cite encyclopedia | title =Time | encyclopedia = Encyclopædia Britannica. Encyclopædia Britannica Online Library Edition | url = http://library.eb.com.au/eb/article-61027| access-date = 20 November 2013 |quote=The use of AM or PM to designate either noon or midnight can cause ambiguity.}} {{subscription required}}</ref><ref name=NISTFAQ/> Each period consists of 12&nbsp;hours numbered: 12 (acting as 0),<ref>{{Cite web |url=http://www.math.csusb.edu/faculty/susan/number_bracelets/mod_arith.html |title=Modular Arithmetic |date=25 August 2016 |access-date=28 November 2008 |first=Susan |last=Addington |archive-url=https://web.archive.org/web/20080704121745/http://www.math.csusb.edu/faculty/susan/number_bracelets/mod_arith.html |archive-date=4 July 2008 |url-status=dead }}</ref> 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The 12-hour clock has been developed since the [[second millennium BC]] and reached its modern form in the 16th century. 

The 12-hour time convention is common in several English-speaking nations and former [[British Empire|British colonies]], as well as a few other countries. In English-speaking countries: "12&nbsp;p.m." usually indicates noon, while "12&nbsp;a.m." means midnight, but the reverse convention has also been used (see [[#Confusion at noon and midnight|§&nbsp;Confusion at noon and midnight]]).<ref>{{Cite web |title=Is noon 12 am or 12 pm? |url=https://www.rmg.co.uk/stories/topics/noon-12-am-or-12-pm |access-date=2023-01-26 |website=Royal Museums Greenwich |language=en}}</ref><ref>{{Cite web |title=U.S. Government Printing Office Style Manual - Chapter 12 - Numerals |url=https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/html/GPO-STYLEMANUAL-2008-14.htm |access-date=2023-01-27 |website=govinfo.gov}}</ref><ref>{{Cite web |date=2020-10-22 |title=time of day, elapsed time |url=https://www.noslangues-ourlanguages.gc.ca/en/writing-tips-plus/time-of-day-elapsed-time |access-date=2023-01-27 |website=Resources of the Language Portal of Canada}}</ref> "Noon" and "midnight" are unambiguous.

{| align="right" class="wikitable" style="margin: 0 0 2em 2em; font-size: 95%"
|+ Clock system
|-
!24-hour clock !! 12-hour clock
|-
| 00:00||midnight<br />12:00&nbsp;a.m.{{Efn|name=noonmidnight}}<br>(start of the day)
|-
| 01:00||1:00&nbsp;a.m.
|-
| 02:00||2:00&nbsp;a.m.
|-
| 03:00||3:00&nbsp;a.m.
|-
| 04:00||4:00&nbsp;a.m.
|-
| 05:00||5:00&nbsp;a.m.
|-
| 06:00||6:00&nbsp;a.m.
|-
| 07:00||7:00&nbsp;a.m.
|-
| 08:00||8:00&nbsp;a.m.
|-
| 09:00||9:00&nbsp;a.m.
|-
| 10:00||10:00&nbsp;a.m.
|-
| 11:00||11:00&nbsp;a.m.
|-
| 12:00||noon<br />12:00&nbsp;p.m.{{Efn|See: {{section link|12-hour clock|Confusion at noon and midnight}}|name=noonmidnight}}
|-
| 13:00||1:00&nbsp;p.m.
|-
| 14:00||2:00&nbsp;p.m.
|-
| 15:00||3:00&nbsp;p.m.
|-
| 16:00||4:00&nbsp;p.m.
|-
| 17:00||5:00&nbsp;p.m.
|-
| 18:00||6:00&nbsp;p.m.
|-
| 19:00||7:00&nbsp;p.m.
|-
| 20:00||8:00&nbsp;p.m.
|-
| 21:00||9:00&nbsp;p.m.
|-
| 22:00||10:00&nbsp;p.m.
|-
| 23:00||11:00&nbsp;p.m.
|-
| 24:00<br>00:00||midnight<br />12:00&nbsp;a.m.{{Efn|name=noonmidnight}}<br>(end of the day)<br>(start of the next day)
|-
|colspan="3"| {{notelist}}
|}