12 a.m. or 12 p.m?

When is 12 a.m.? When is 12 p.m.?


12AM is midnight. 12pm is noon.

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?

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.

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.

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.

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.

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.

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.

Of course, what’s in between is 12:00:00 m., which, alas, many folks believe stands for midnight.

Then there are leap seconds, so you can have 23:59:60 UTC in between 23:59:59 UTC and 00:00:00 UTC.

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).

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.

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. 12:00 a.m.

LOL! Q. “What happened at 12:00 PM on December 31, 1999?”
A. “The clock sounded 12:00 Noon.”


Moderator’s Note: Moving to IMHO.

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