What is the full form of AM and PM

AM: Anti Meridiem, PM: Post Meridiem

Do you ever wonder why we denote time in terms of AM and PM? What do AM and PM stand for? From where did this way of denoting time originate? If the answer to any of these questions is yes, then you have reached your destination. Before understanding what AM and PM mean in the context of the 12-hour clock system, it is important to understand the 12-hour clock system first. The 12-hour clock system is a time convention used mainly in most analogue and digital clocks. This is a popular way to read time in most English-speaking nations and the then British colonies. The 12-hour clock convention is the one in which 24 hours are divided into two periods- AM and PM. 

Full form of AM and PM in detail

AM and PM are both Latin terms used to represent time in the 12-hour convention. A.M. stands for Ante Meridiem and P.M. stands for Post Meridiem. Meridiem is a Latin word that basically means midday (Meri means mid and Diem means day). Hence, Ante Meridiem means “before midday” and Post Meridiem means “after midday”. In the 12-hour clock system, AM and PM are used before noon and afternoon respectively. 

Fun Fact: It might be interesting to know that a 12-hour clock system is not a new concept. Even during ancient times, Egyptians and Mesopotamians used it in primitive forms. For instance, the Egyptian sun-dial clock for daytime use and Egyptian water clock for night-time use were found in the tomb of a Pharaoh. 

To understand this system of denoting time, you can simply look at it as two different time zones of 12 hours each that represent day and night. Basically, 24 hours are divided into two time zones (before noon and afternoon) that last for 12 hours each.  The first 12-hour duration starts from midnight and lasts till noon which is called by AM (12 AM to 12 PM). The second 12-hour duration begins from noon and lasts till midnight denoted by PM (12 PM to 12 AM). 

Let us understand this with the help of examples. When someone says it’s 9 AM, it means that the time is 9 O’Clock in the morning. So, from 12 at night to 12 in the noon (exactly at 11:59 AM), it represents the day clock. Similarly, when someone says it is 9 PM, it means that the time is 9 O’Clock in the evening. Hence, from 12 in the noon to 12 at midnight (precisely,11:59 PM), it is the night clock. 

These conventions are set up to understand time in a better manner. Suppose, if someone says that he/she will meet you at 8 O’Clock tomorrow, it will be confusing whether that person meant 8 in the morning or 8 in the evening. To avoid such time-related confusion, the 24-hour daytime is divided into two different cycles of 12 hours each. Moreover, another confusion that is quite common is to understand 12 AM and 12 PM, also these are not technically correct. There is no such thing as 12 AM or 12 PM. It is actually called 12 in the noon (12 PM) and 12 at midnight (12 AM). To avoid confusion, many companies including some airlines and banks, etc. use 12:01 AM to mark the beginning of an event that starts with the onset of the day and 11:59 PM to mark the end of any event that ends with the day.

In some countries like the USA and Canada Military timing is used which works on the 24-hour clock system. This system completely rules out the possibility of using AM and PM, thereby eliminating confusion altogether. Here, the entire day is divided into 24 hours. It is important you know both the systems and understand how they can be interconverted. Comparison between the two can be understood by the following table:

24-hour Clock System	12-hour Clock System
00:00	12:00 AM
01:00	1:00 AM
02:00	2:00 AM
03:00	3:00 AM
04:00	4:00 AM
05:00	5:00 AM
06:00	6:00 AM
07:00	7:00 AM
08:00	8:00 AM
09:00	9:00 AM
10:00	10:00 AM
11:00	11:00 AM
12:00	12:00 PM
13:00	1:00 PM
14:00	2:00 PM
15:00	3:00 PM
16:00	4:00 PM
17:00	5:00 PM
18:00	6:00 PM
19:00	7:00 PM
20:00	8:00 PM
21:00	9:00 PM
22:00	10:00 PM
23:00	11:00 PM

Time is an entity that has generated curiosity among Humans since time Immemorial. But the Human mind has always been troubled with the way time and related concepts work. To understand time better, you can refer to IMP’s explanation of time. It will help you a lot in subjects like mathematics and geography. 

The concept of AM and PM is not just relevant in academics but also holds a lot of significance in daily life. Vedantu hopes you enjoyed reading this article on AM and PM, learnt something new and also got all your doubts cleared about the same.