# 12 a.m. or 12 p.m? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [October 23, 2004, 12:51pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758 "2004-10-23T12:51:41Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [October 23, 2004, 12:51pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/1 "2004-10-23T12:51:41Z")
When is 12 a.m.? When is 12 p.m.? ---
**Author:** ![rfgdxm](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rfgdxm](https://boards.straightdope.com/u/rfgdxm)\ **Post date:** [October 23, 2004, 12:54pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/2 "2004-10-23T12:54:16Z")
> [@Ignatz](#): > > When is 12 a.m.? When is 12 p.m.? ??? ---
**Author:** ![Brutus](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@Brutus](https://boards.straightdope.com/u/Brutus)\ **Post date:** [October 23, 2004, 12:59pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/3 "2004-10-23T12:59:55Z")
12AM is midnight. 12pm is noon. ---
**Author:** ![elfkin477](https://avatars.discourse-cdn.com/v4/letter/e/a9a28c/32.png) [@elfkin477](https://boards.straightdope.com/u/elfkin477)\ **Post date:** [October 23, 2004, 1:00pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/4 "2004-10-23T13:00:41Z")
> [@Ignatz](#): > > When is 12 a.m.? When is 12 p.m.? 12 pm is 1200 hours. 12 am is 2400 hours (though I’ve seen it expressed as 0000 hours as well). Was this meant for general questions? ---
**Author:** ![rfgdxm](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rfgdxm](https://boards.straightdope.com/u/rfgdxm)\ **Post date:** [October 23, 2004, 1:08pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/5 "2004-10-23T13:08:30Z")
> [@elfkin477](#): > > 12 pm is 1200 hours. 12 am is 2400 hours (though I’ve seen it expressed as 0000 hours as well). Midnight per the international standard is 0000 hours. Try listening to the shortwave time and frequency stations, and they all call it 0000 hours. Even on my Windows box after 2359 it switches to 0000. ---
**Author:** ![ParentalAdvisory](https://avatars.discourse-cdn.com/v4/letter/p/53a042/32.png) [@ParentalAdvisory](https://boards.straightdope.com/u/ParentalAdvisory)\ **Post date:** [October 23, 2004, 1:12pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/6 "2004-10-23T13:12:30Z")
12:00am can also be 36:00 hrs, and 12:00pm can be 48:00 hrs if you’re scheduling into the next day. Um, yeah, good luck with this. ---
**Author:** ![1010011010](https://avatars.discourse-cdn.com/v4/letter/1/ea666f/32.png) [@1010011010](https://boards.straightdope.com/u/1010011010)\ **Post date:** [October 23, 2004, 1:45pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/7 "2004-10-23T13:45:22Z")
I noticed that whenever people do the daily log continuation… Midnight is 2400 on the logs being closed and 0000 on the logs being started. Tribal knowledge thing, though, so I don’t know if there’s any “official” instruction on the matter. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [October 23, 2004, 2:24pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/8 "2004-10-23T14:24:44Z")
Of course, noon _should_ be 12:00 **m**. and midnight could then be either a.m. or p.m. equally, but it is too much for the modern mind to comprehend the nature of _ante_, _post_, and _meridiem_, so we associate midnight with the beginning of the new day and noon with the beginning of the second half of the day and assign, by _convention_ a.m. to midnight and p.m to noon. ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [October 23, 2004, 3:14pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/9 "2004-10-23T15:14:17Z")
> [@tomndebb](#): > > Of course, noon _should_ be 12:00 **m**. and midnight could then be either a.m. or p.m. equally, but it is too much for the modern mind to comprehend the nature of _ante_, _post_, and _meridiem_, so we associate midnight with the beginning of the new day and noon with the beginning of the second half of the day and assign, by _convention_ a.m. to midnight and p.m to noon. Clearly debatable, rather than general question category. You are the only one that got it right. a.m. is the abbreviation for the Latin \*ante meridiem \* meaning before noon and p.m. is for \*post meridiem \* meaning after noon, ergo, they both mean midnight, technically. I agree it is “too much…to comprehend…” I use “military” time, 0000 to 2400, as much as possible. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [October 23, 2004, 3:19pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/10 "2004-10-23T15:19:20Z")
What Tom says is on target. Because there is so much confusion about this (and I’ve seen explicit usage guides that make noon 12 AM and midnight 12 PM, the reverse of what’s said here), it’s usually considered preferable to reference the exact hours as 12 Noon and 12 Midnight rather than applying an abbreviation which fits neither. (Technically, midnight would be both 12:00 AM and 12:00 PM – i.e., twelve hours and no minutes **before** and also **after** noon, the literal meanings of AM and PM.) One second before noon is 11:59:59 **AM** , and one second after is 12:00:01 **PM**. What’s in between is neither before nor after noon, so neither coding really fits. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [October 23, 2004, 3:25pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/11 "2004-10-23T15:25:23Z")
Johnny Carson once had as a guest a guy who got a ticket for illegal parking when the sign said something about no parking after 12pm. He argued the sign was ambiguous, and Carson phoned an astronomer at the observatory at Greenwich who agreed. I don’t remember whether the guy was able to get the ticket dismissed. ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [October 23, 2004, 3:44pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/12 "2004-10-23T15:44:28Z")
> [@Polycarp](#): > > What Tom says is on target. Because there is so much confusion about this (and I’ve seen explicit usage guides that make noon 12 AM and midnight 12 PM, the reverse of what’s said here), it’s usually considered preferable to reference the exact hours as 12 Noon and 12 Midnight rather than applying an abbreviation which fits neither. (Technically, midnight would be both 12:00 AM and 12:00 PM – i.e., twelve hours and no minutes **before** and also **after** noon, the literal meanings of AM and PM.) > > One second before noon is 11:59:59 **AM** , and one second after is 12:00:01 **PM**. What’s in between is neither before nor after noon, so neither coding really fits. Of course, what’s in between is 12:00:00 m., which, alas, many folks believe stands for midnight. ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [October 23, 2004, 4:47pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/13 "2004-10-23T16:47:14Z")
> [@Polycarp](#): > > One second before noon is 11:59:59 **AM** , and one second after is 12:00:01 **PM**. What’s in between is neither before nor after noon, so neither coding really fits. Then there are leap seconds, so you can have 23:59:60 UTC in between 23:59:59 UTC and 00:00:00 UTC. ---
**Author:** ![Valgard](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Valgard](https://boards.straightdope.com/u/Valgard)\ **Post date:** [October 23, 2004, 6:58pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/14 "2004-10-23T18:58:12Z")
> [@Dewey Finn](#): > > Johnny Carson once had as a guest a guy who got a ticket for illegal parking when the sign said something about no parking after 12pm. He argued the sign was ambiguous, and Carson phoned an astronomer at the observatory at Greenwich who agreed. I don’t remember whether the guy was able to get the ticket dismissed. I remember that show and have had this debate with my friends. Despite being otherwise intelligent they claim that 12:00am means noon and 12:00pm means midnight…or is it the other way around? [grin] Seriously, I can never figure out whether to use am or pm so I always say 12 Noon and 12 Midnight. Clear, unambiguous and it’d pass muster on a frickin’ parking sign. What is so hard about this? Not a big deal in most parts of life but when I’m scheduling a server outage I want to be really specific so I say midnight or noon (or sometimes resort to 11:59pm instead of midnight so there’s no confusion). ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [October 23, 2004, 10:30pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/15 "2004-10-23T22:30:24Z")
Exactly 12:00Noon is exactly that and exactly 12:00Midnight is also exactly that. Neither are AM or PM. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [October 23, 2004, 11:30pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/16 "2004-10-23T23:30:58Z")
> [@DrDeth](#): > > Exactly 12:00Noon is exactly that and exactly 12:00Midnight is also exactly that. Neither are AM or PM. Except that the “12:00” is redundant; noon or midnight by themselves are sufficient. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [October 23, 2004, 11:35pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/17 "2004-10-23T23:35:36Z")
Much like the debate on the Millennium, thebattles over noon and midnight could rage for a long time. While it may be comfortable to declare that 12:00 can never _really_ be a.m. or p.m., the reality is that people do indicate time using a.m. and p.m. associated with 12:00. The convention is inconsistent, as **Polycarp** noted, but we still have a convention and it is futile to declare that it does not exist: [12:00 p.m.](http://www.google.com/search?hl=en&lr=&safe=off&c2coff=1&q=12%3A00+p+m) [12:00 a.m.](http://www.google.com/search?hl=en&lr=&safe=off&c2coff=1&q=12%3A00+a+m&btnG=Search) ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [October 23, 2004, 11:40pm UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/18 "2004-10-23T23:40:44Z")
> [@tomndebb](#): > > Much like the debate on the Millennium, thebattles over noon and midnight could rage for a long time. > > While it may be comfortable to declare that 12:00 can never _really_ be a.m. or p.m., the reality is that people do indicate time using a.m. and p.m. associated with 12:00. The convention is inconsistent, as **Polycarp** noted, but we still have a convention and it is futile to declare that it does not exist: > [12:00 p.m.](http://www.google.com/search?hl=en&lr=&safe=off&c2coff=1&q=12%3A00+p+m) [12:00 a.m.](http://www.google.com/search?hl=en&lr=&safe=off&c2coff=1&q=12%3A00+a+m&btnG=Search) LOL! Q. “What happened at 12:00 PM on December 31, 1999?” A. “The clock sounded 12:00 Noon.” :smack: ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [October 24, 2004, 12:00am UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/19 "2004-10-24T00:00:04Z")
**Moderator’s Note:** Moving to IMHO. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [October 24, 2004, 2:19am UTC](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758/20 "2004-10-24T02:19:20Z")
since from midnight + 1 second to m + 59 seconds is AM, it makes a marginal amount of sense to declare midnight AM (since most often you are rounding to the minute anyway) ditto for noon being PM. here is NISTs answer: [http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-57026](http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-57026) Brian [Next page](https://boards.straightdope.com/t/12-a-m-or-12-p-m/270758.md?page=2)