Tuesday, October 25, 2011

24-hour system


Time - 12-hour system (AM/PM) vs 24-hour System

Normally the time is shown as Hours:Minutes
There are 24 Hours in a Day and 60 Minutes in each Hour.
Example: 10:25 means 10 Hours and 25 Minutes

Showing the Time

There are two major ways to show the time: "24-hour system" or "12-hour system AM/PM".

  • With the 24-hour system the time is shown as how many hours and minutes since midnight.
  • With AM/PM (or "12-hour system") the day is split into the 12 Hours running from Midnight to Noon (the AM hours) and the other 12 Hours running from Noon to Midnight (the PM hours).


Ante Meridiem*
Latin for "before midday"
Post Meridiem*
Latin for "after midday"
Midnight to Noon
Noon to Midnight
24-hour system:
0:00 to 11:59
12:00 to 23:59

*Is that spelled "Meridiem" or "Meridian"?

"Meridiem" vs "Meridian"
Should "AM" be "ante meridiem" or "ante meridian" (likewise for PM)?
The official (according to an American, Australian and British dictionary I checked), and most common spelling for AM is "ante meridiem" which is a Latin phrase. I recommend that spelling!
But people sometimes use the phrase "ante meridian" (a "meridian" in this case refers to an imaginary line in the sky when the sun is at its highest point).

1 comment:

  1. Until now i just know the full words of am and pm. It quite difficult to remember the spelling.