Although most countries around the world observe the 24-hour system, there are a lot of countries where 12-hour format time is also used. 12-hour periods are often designated as a.m. and p.m., especially in English-speaking countries. What they mean and how to convert time in 12-hour format to 24-hour, we will tell in this article.
PM and AM meanings
AM and PM mean what half of the day it is. They divide the day in halfs:
- m. is the time from 00:01 to 11:59;
- m. is the time from 12:01 to 23:59.
What do the abbreviations stand for?
These abbreviations have Latin origin:
- AM means “Ante meridiem” that is translated as “Before noon” or “Before midday”.
- PM means “Post meridiem” that is translated as “After noon” or “After midday”.
Spelling and grammar
Likely you come across such spellings of ante meridiem and post meridiem:
- AM/PM
- am/pm
- m./p.m.
- M./P.M.
All of them are equally correct and widely used, but due to some guides it is better to write lowercased and separated by periods like that: a.m. and p.m.
AM&PM: midnight or noon?
12-hour format has a weakness, which confuses people. We mean those two minutes a day that fall at noon (12:00) and midnight (00:00). Which of them refers to a.m., and which to p.m.? None of them refers to the moment before noon (am) or after noon (pm).
The most common decision is to designate 12 a.m. for midnight and 12 p.m. for noon. However, to avoid confusion in these two cases, you should make an exception and say/write 12 noon or 12 midnight instead of a.m. and p.m.
If an event is scheduled for 12 midnight, be sure to clarify the date. Otherwise, you may be confused whether 12 a.m. means one’s midnight or another — depending on how you understand time.
How to convert 24-hour to 12-hour format?
| 12-hour clock format | 24-hour clock format |
| 12:00 a.m./12 o’clock a.m./12:00 midnight | 00:00/24:00 |
| 1:00 a.m./1 o’clock a.m. | 01:00 |
| 2:00 a.m./2 o’clock a.m. | 02:00 |
| 3:00 a.m./3 o’clock a.m. | 03:00 |
| 4:00 a.m./4 o’clock a.m. | 04:00 |
| 5:00 a.m./5 o’clock a.m. | 05:00 |
| 6:00 a.m./6 o’clock a.m. | 06:00 |
| 7:00 a.m./7 o’clock a.m. | 07:00 |
| 8:00 a.m./8 o’clock a.m. | 08:00 |
| 9:00 a.m./9 o’clock a.m. | 09:00 |
| 10:00 a.m./10 o’clock a.m. | 10:00 |
| 11:00 a.m./11 o’clock a.m. | 11:00 |
| 12:00 p.m./12 o’clock p.m./ 12:00 noon | 12:00 |
| 1:00 p.m./1 o’clock p.m. | 13:00 |
| 2:00 p.m./2 o’clock p.m. | 14:00 |
| 3:00 p.m./3 o’clock p.m. | 15:00 |
| 4:00 p.m./4 o’clock p.m. | 16:00 |
| 5:00 p.m./5 o’clock p.m. | 17:00 |
| 6:00 p.m./6 o’clock p.m. | 18:00 |
| 7:00 p.m./7 o’clock p.m. | 19:00 |
| 8:00 p.m./8 o’clock p.m. | 20:00 |
| 9:00 p.m./9 o’clock p.m. | 21:00 |
| 10:00 p.m./10 o’clock p.m. | 22:00 |
| 11:00 p.m./11 o’clock p.m. | 23:00 |
Converting 24 hour to 12 hour and vice versa is quite simple.
For converting 12-hour to 24-hour time you should count in such a way:
- From 12:00–12:59 a.m. you must subtract 12 hours;
- The time from 1:00 a.m. to 11:59 a.m. is the same in 24-hour format;
- The time 12:00–12:59 p.m. is the same in 24-hour format;
- Add 12 hours to 1:00–11:59 p.m. to convert time format.
24 hour to 12 hour convert somewhere needs opposite calculations and somewhere is the same:
- The time from 01:00 to 12:59 is the same.
- The time from 13:00 to 23:59 is calculated by subtracting 12 hours from necessary time.
- 00:00 or 24:00 is the same as 12 a.m.
- The time from 00:01 to 00:59 is calculated by adding 12 hours to the time on a clock.
Where is the 12-hour time format used?
International time format means using the 24-hour system. However, the 12-hour format, including a.m. and p.m. designations is still officially used in such countries as:
- Australia;
- Bangladesh;
- Canada (except Québec);
- Egypt;
- India;
- Lebanon;
- Malaysia;
- Malta;
- Mexico;
- Nepal;
- New Zealand;
- Pakistan;
- the Philippines;
- Republic of Ireland;
- South Africa;
- the United States;
- the United Kingdom of Great Britain.
In several countries the 12-hour clock format is the dominant in writing and speaking, but in most countries the 24-hour clock is still the standard system.
A combination of the two formats is preferable in some countries of Europe and Latin America. 12-hour system is mostly used in speech there. However, in written form and in formal contexts people use the 24-hour system.