What do AM and PM mean? They split the day into two halves: AM = before noon, PM = after noon. The terms come from Latin. Here's the full explanation — including the confusing case of noon and midnight.
For the current time anywhere, see the world clock.
What AM and PM stand for
Both are abbreviations of Latin phrases referring to midday (meridiem):
- *AM = ante meridiem*** — "before midday"
- *PM = post meridiem*** — "after midday"
The 12-hour clock divides the 24-hour day into two 12-hour periods: the AM half (midnight to noon) and the PM half (noon to midnight).
Is noon 12 PM or 12 AM?
This is the part that trips everyone up. By the most widely used convention:
- 12:00 noon = 12 PM
- 12:00 midnight = 12 AM
But because this is genuinely ambiguous (12 "before/after midday" doesn't quite make sense at the boundary), many official sources avoid "12 AM/PM" entirely and write "12 noon" and "12 midnight", or use the 24-hour clock (12:00 and 00:00).
AM/PM to 24-hour clock
| 12-hour | 24-hour |
|---|---|
| 12:00 AM (midnight) | 00:00 |
| 1:00 AM | 01:00 |
| 11:00 AM | 11:00 |
| 12:00 PM (noon) | 12:00 |
| 1:00 PM | 13:00 |
| 11:00 PM | 23:00 |
See the 24-hour clock explained for the full conversion.
Quick answers
What does AM mean? "Ante meridiem" — Latin for "before midday." It covers midnight to just before noon.
What does PM mean? "Post meridiem" — Latin for "after midday." It covers noon to just before midnight.
Is noon 12 PM or 12 AM? By the common convention, noon is 12 PM and midnight is 12 AM — but many sources write "12 noon" and "12 midnight" to avoid confusion.
What is 12 AM and 12 PM? 12 AM is midnight; 12 PM is noon.