Man schreibt es 12 Uhr und spricht es genauso aus.

http://en.wikipedia.org/wiki/Noon#Nomenclature

Assuming you mean midnight, that is 0:00 Uhr / Null Uhr (or Mitternacht) in German. http://de.wikipedia.org/wiki/Mitternacht

Let's be clear though: 12:00 AM is noon, not midnight.

Im Alltagsgebrauch wird das 24-Std-System nicht durchgängig verwendet. Wenn es im Kontext zweifelsfrei klar ist, welcher Zeitpunkt gemeint ist, dann kann man auch "Zwölf Uhr" sagen. Selbst, wenn "12 Uhr nachts" gemeint ist.

"12 Uhr nachts am Montag" ist "00:00 Uhr" des Dienstag.

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Nachtrag:

Steve, diese Frage ist ein immerwährender Quell der Freude... Die angelsächsische Welt scheint sich nicht einig:

Laut Wikipedia:

Digital clocks and computers commonly display 12 p.m. for noon.

The 30th edition of the U.S. Government Style Manual (2008) sections 9.54 and 12.9b recommends the use of "12 a.m." for midnight and "12 p.m." for noon.[4][5][nb 1]

The 29th edition of the U.S. Government Printing Office Style Manual (2000) section 12.9 recommended the opposite the use of "12 p.m." for midnight and "12 a.m." (formerly "12 m.") for noon.

Streng genommen sind Mittag und Mitternacht weder a.m. noch p.m. Wenn es sich nicht aus dem Zusammenhang eindeutig ergibt, sagt man eben Midnight / Noon ("12 m." kannte ich nicht, finde ich gut, ist aber nicht weit genug verbreitet).

In der Praxis bedeutet mit einiger Wahrscheinlichkeit 12 p.m. Mittag and 12 a.m. Mitternacht.

Most style guides say that either "12 a.m." or "12 p.m." are nonsense, as 12:00 is the meridian, so can't be before or after it, which is what a.m. and p.m. mean. They recommend using "(12) noon" and "(12) midnight". 12.01 a.m. is then one minute after midnight and 12.01 p.m. is one minute after noon.
In practice people use both versions for midday/midnight, as the US government example shows so nicely :-)

Please please please can we just forget that I posted no. 3??? What a f***wit....:-)

(Version no. 30 of the US gvmt. manual is the standard practice, of course. Thank you all for being so polite about it!)

12a.m = 12 Uhr
12p.m.= 0 Uhr

Is so bleibt so

Nach sechs Wochen ausgiebigem Studium von Busfahrplänen in Sydney kann ich mit Bestimmtheit sagen:

12 pm = Mittag
12 am = Mitternacht

Monday 7.30am -9.30am, 12.00pm - 7.00pm http://www.bris.ac.uk/sport/facilities/swimmi...

Wednesdays 11.00am - 12.00pm Free Childrens Activities http://www.powys.gov.uk/index.php?id=2503&L=0

University of East Anglia Law Fair - 12.00pm to 4.00pm http://www.addleshawgoddard.com/graduates/vie...

Time: 12.00pm to 4.00pm = Women Only. http://www.google.co.uk/url?sa=t&source=web&c...

12.00am to 2.00pm. Senior Citizen Dance. http://www.google.co.uk/url?sa=t&source=web&c...

The 2006 traffic survey showed 10.00 -12.00 a.m. to be the busiest morning period. http://www.google.co.uk/url?sa=t&source=web&c...

The Bookshop is open at the following times:
Sunday: 12.00 am to 5.00 pm http://www.alumni.ox.ac.uk/benefits/oxford_al...

Our lunchtime is:- 12.00am to 1.15pm. http://www.seatoninf.cumbria.sch.uk/index.php...

In real life there's no consensus, and it saves confusion just to avoid them.

#10: In real life there's no consensus, and it saves confusion just to avoid them.

The problem is that UK/US/Oz don't avoid them :-).
In OZ 0:00 Uhr is 12 am.

#11 Mostly it makes no difference whether you write it as a.m. or p.m., as usually it's clear whether something is likely to end at midnight or lunchtime, either from the nature of the event or from the time it starts.
The only time you need to be really careful is when it isn't clear - and in that case it's not a good idea to use either, as even if some style guide somewhere says that Australians use 12 a.m. for midnight, even Australians are not going to agree on that. http://www.google.co.uk/search?hl=en&esrch=Be...

This has come up many, many times in the forum, and each time I am astonished that there are actually people who don't know that 12 pm is noon and 12 am is midnight. If you're still skeptical, you can prove this just by checking any 12-hour digital clock, like your bedside alarm clock or the clock on your telephone answering machine. You will notice that it changes from am to pm when it reaches the 12 o'clock hour, and when you think about it, that's only sensible, because all the minutes within that hour belong to it.

Neither the US government nor Wikipedia is a particularly reliable source.

it changes from am to pm when it reaches the 12 o'clock hour, and when you think about it, that's only sensible, because all the minutes within that hour belong to it.

Ah, but what about 12:00:00 sharp? Is that really "post meridiem"? Yes, it will be one second later, and yes, I might be splitting hairs here, just playing devil's advocate.

I'm glad I'm not the only one who was slightly confused by this at first. I felt like such a moron when I had to ask my husband to make sure I set my alarm clock right (it was after midnight and I wasn't sure if the little red "P.M." light was supposed to be on or off) Answer: Midnight is 12 A.M.

Now I think of the Eric Clapton song "After Midnight" -> A.M.