Describe and Convert the Difference Between the Ante Meridiem (a.m.) and Post Meridiem (p.m) System of Time (12 Hour Clock) and the 24-Hour Clock

In healthcare, the 24-hour clock is often used instead of the Latin system using ante meridiem (a.m.) and post meridiem (p.m.). Using the a.m. and p.m. notation when communicating about time can be confusing and lead to errors in places that function during the night and day. Instead of having time be broken into two periods of 12 hours each, each hour of the day is noted with its number the clock being a 24-hour clock. The 24-hour clock starts counting at 12 a.m., or midnight, at 0000. 1 a.m. is written as 0100, 2 a.m. is written as 0200, 1 p.m. is written as 1300. To determine how to write p.m. times, all you need to do is add 1200 to any notation of p.m. time.

3:00 p.m. = 1500 hours

Eventually, using the 24-hour clock will become habitual, and you will not have to think about how to convert between the two systems at all. You can also refer to the table below as a quick reference to see what each hour of p.m. time is in the 24-hour system. You never have to change how minutes are recorded. Some professions continue to use a colon when writing times using the 24-hour system, but in handwritten healthcare charting the colons are generally left out to keep charting entries clear. Computer systems will often use colons, especially if there are seconds also being recorded.