Noon or Midnight?

A question frequently asked is whether 12 AM and 12 PM should be used to denote noon and midnight, respectively, or vice versa. The answer is that these abbreviations should not be used. They will cause confusion.

The abbreviation 12m is sometimes used to denote noon (m denotes meridian). However, 12m is likely to be interpreted as an abbreviation for midnight. Hence, 12m should not be used either.

The following are three solutions to the problem of designating noon and midnight unambiguously:

  1. Use the complete words “noon” and “midnight”. If midnight is used give the two dates between which it falls. Thus, for example, “midnight of 21 September” is ambiguous but “midnight of 21/22 September” is specific.
  2. Prepare schedules with times other than noon and midnight. Use times such as 12:01 AM, 11:59 PM, etc. This is done by railroads.
  3. Use the 2400 system, which is used by international airlines and the military services. The first two digits give the hours past midnight and the second two give the minutes. Noon is designated by 1200. Midnight is designated as 0000 of the new date, i.e., midnight of 21/22 September is 0h, 22 September.


It has often been proposed to decide by law or regulation the proper designation of noon and midnight. This has in fact been attempted. This has not, however, removed the ambiguity and resulting confusion. The Government Printing Office Style Manual states that noon is 12AM.

All the digital watches, however, disregard this and switch to PM at the moment they come to 12:00:00. It is clear that a regulation is powerless to override an inherent ambiguity.