The 12-hour system divides the 24 hours of the day into two 12-hour sections. Am is the first 12-hour period of the day. It lasts from 12 a.m. until 12 p.m. The second time period, designated as pm, spans 12 hours from midday to midnight.

The abbreviations am and pm are Latin abbreviations:

Ante meridiem is Latin for “before noon.”

PM stands for “post meridiem,” which means “afternoon.”

The 12-hour clock system indicates all 24 hours of the day by using digits from 1 to 12, followed by am or pm. 5 a.m. is early in the morning, and 5 p.m. is late in the afternoon; 1 a.m. is one hour after midnight, and 11 p.m. is one hour before midnight, for example.

The abbreviation for ante meridiem is AM, and the abbreviation for post meridiem is PM., like many other sources, uses am and pm, but the other variations are equally correct and widely used.

In which country am and pm are used most commonly

The 12-hour clock format, which includes am and pm, is used in some nations, including the United States, Canada, and Australia. The 24-hour system is now used in almost every country on the planet. However, a number of countries, including the United States, Canada (excluding Québec), Australia, New Zealand, and the Philippines, adopt the 12-hour schedule, which has am and pm.

When to use am and pm

AM or PM at Midnight and Noon?

The 12-hour system’s fundamental flaw is widespread ambiguity about which abbreviation to use for noon and midnight: neither moment can be rationally classified as before noon (am) or afternoon (pm) (pm). Midnight, for example, happens exactly 12 hours afternoon on the previous day and 12 hours before noon on the following day.

Most digital clocks and sites, including, refer to midnight as 12 a.m. and noon as 12 p.m., respectively. Although the exact time of noon falls into neither of these categories, the hour after it, from 12:00:01 to 12:59:59, is unmistakably afternoon.

We propose instead using the identifiers 12 noon and 12 midnight to avoid any confusion when referring to the specific moment of noon or midnight.

Ways people write am and pm

Ante meridiem is commonly denoted as AM, am, a.m., or A.M.; post meridiem is usually abbreviated PM, pm, p.m., or P.M. Like many other sources, uses am and pm, but the other variants are equally correct and widely used.

Why 12-hour clock is necessary

The natural division of a calendar day into day and night is the underlying reason why each day is divided into two cycles. There were originally two cycles: one that could be observed by the position of the Sun (day), and another that could be tracked by the Moon and stars (night). This gradually evolved into the two 12-hour periods used today, one beginning at midnight and ending at noon, which is referred to as “a.m.” and “p.m.” respectively. Noon is rarely abbreviated nowadays, but when it occurs, it is signified by the letter “m.”

24 hours Vs 12 hours comparison

The difference between a 12-hour clock and a 24-hour clock is merely in the way they are expressed; both are time conventions, with the former splitting the day into two periods and the latter counting the entire 24 hours of the day continuously. Essentially, the two-time protocols are interchangeable, with certain portions of the world employing both and others favouring one over the other.