Time is an integral part of everyday life. It can be used to plan day-to-day activities, such as meals, work and social meetings. The ancient world didn't have a standard way of telling time, which meant that different civilizations had to try and work out their own method of understanding the passage of time. However, the modern world has a standard time system across the globe that ensures different countries are following the same
There are two main international systems for telling time. They work on a 12-hour and 24-hour time basis. These systems use digital and analog clocks, which can tell people how many hours, minutes, and seconds have passed each day and night.
The 12-hour clock means that the 24-hour day is divided into two 12-hour segments. Based on this system, the 12 hours proceeding midday are referred to using 'AM', which is Latin for ante meridiem. This translates to 'before midday' in English and means that the sun has yet to cross the meridian (a longitude circle around the Earth that passes through the North and South poles). 'PM' is Latin for post meridiem which translates to 'after midday' and describes the hours after the sun has crossed the meridian.
In this article, we'll look at how you can easily convert time between 12-hour clocks and 24-hour clocks, as well as the origin of both systems and how they are used differently in various countries and industries.
The 12-hour clock is used in most English-speaking countries, including the US and UK. Each day is divided into two lots of 12, starting from 12 AM (midnight). Each hour consists of 60 minutes, whilst each minute consists of 60 seconds.
The format for the 12-hour clock is HH:MM AM/PM or HH:MM:SS AM/PM, where H = hours, M = minutes, and S = seconds. The minutes and seconds will remain the same, whether you use a 12-hour or 24-hour clock. For example, half-past eight will still include 30 minutes, whether it is written as 8:30 PM or 20:30.
The first hour of the morning runs from midnight through to 12 midday. From this point on, the time resets for the afternoon and counts from 1 to 12 again, starting at 1 PM. The day ends just before midnight at 11:59 PM.
The addition of AM and PM is important in the 12-hour clock as it tells you whether the time refers to the morning or afternoon. However, analog clocks only show 12 hours, which means that there is no way to differentiate between times such as 1 AM and 1 PM when reading a clock face. 12-hour digital clocks usually feature AM and PM hours to help users determine the exact time of day if they haven't got additional context to know whether it is during the day or night.
Due to the potential confusion caused by 12-hour clocks if no context is given for whether the time refers to AM or PM, 24-hour clocks are often used in areas such as public transport so that passengers know if the train or bus timetable is referring to journeys made in the day or evening.
The 24-hour clock is commonly used in most non-English speaking countries, although it is used interchangeably in English-speaking countries too. Some countries use the 24-hour clock when verbally speaking. For example, an individual from countries such as Germany or France may state that the time is 'fourteen hundred hours' or '14 hours' when referring to 14:00 or 2 PM. However, the 12-hour format is more commonly used in spoken form around the world by native English speakers.
Unlike the 12-hour clock, which 'resets' at midday to begin counting from one through 12 again, the 24-hour clock continues past 12 until 23:59. This means that most analog clocks are 12-hour, although some may feature the additional numbers of 13 through to 23. This is uncommon, however, which means that most 12-hour clocks are analog and 24-hour clocks are digital.
The 24-hour clock means that you don't have to add AM or PM to the end of the time. The time is told using digital means and will feature four digits. All times proceeding midday will feature a zero before the first digit. For example, 2 AM will be read as 02:00. However, your clock may still read AM or PM depending on your settings, even though the digits will clearly indicate whether the time is before or after midday. Two O'clock in the morning would read 02:00, which would indicate the time is prior to midday, but Two O'clock in the afternoon would read 14:00.
Military time
Military time uses the 24-hour clock, which begins at midnight and shows as 00:00. Individuals will verbally refer to the time as 'hundred hours' instead of 'O'clock'. For example, three O'clock in the afternoon would be referred to as 'fifteen hundred hours' and half-past three in the afternoon would be verbally read as 'fifteen thirty'.
Hours that proceed midday are pronounced with a zero in front of the time. For example, 7 AM or 07:00 AM would be referred to as 'zero seven hundred hours'. Following this format, the minutes would be added so that 7:15 AM or 07:15 AM would be referred to as 'zero seven fifteen hours'.
Many movies and TV shows show characters pronouncing military time with an 'oh' in front of the time instead of a zero. For example, 7 AM or 07:00 AM would be pronounced as 'oh seven hundred hours'. However, this is colloquial and not part of standard military protocol when verbally telling the time.
Some military missions may involve personnel crossing time zones, which is why they may need to reference which time zone they are working from. Zulu, sometimes referred to as Zulu time, is used by the military when they are referring to Universal Coordinated Time (UTC). This time (formerly referred to as Greenwich Mean Time (GMT), is the standard time in the world.
Military personnel will add 'Z' or 'zulu' to the end of the time they are saying so that all individuals involved know that the time they are referring to is based on UTC. For example, 2 PM or 14:00 would be pronounced as 'fourteen hundred hours Zulu.
You can easily convert time from the 12-hour clock to the 24-hour clock by adding 12 to the number of hours that are listed after midday. For example:
3pm becomes 15:00 because 3+12 = 15
11pm becomes 23:00 because 11+12 = 23
This method can also be reversed to convert the time on a 24-hour clock to 12-hour. For example:
18:00 becomes 6pm because 18-12 = 6
21:00 becomes 9pm because 21-12 = 9
The table below shows the conversion between the 12-hour and 24-hour clocks. The 24-hour clock runs from 00:00 to 23:00, whereas the 12-hour clock resets to 01:00 after 12:00 AM and 12:00 PM.
| 12-hour clock | 24-hour clock |
| 12:00 AM | 00:00 |
| 01:00 AM | 01:00 |
| 02:00 AM | 02:00 |
| 03:00 AM | 03:00 |
| 04:00 AM | 04:00 |
| 05:00 AM | 05:00 |
| 06:00 AM | 06:00 |
| 07:00 AM | 07:00 |
| 08:00 AM | 08:00 |
| 09:00 AM | 09:00 |
| 10:00 AM | 10:00 |
| 11:00 AM | 11:00 |
| 12:00 PM | 12:00 |
| 01:00 PM | 13:00 |
| 02:00 PM | 14:00 |
| 03:00 PM | 15:00 |
| 04:00 PM | 16:00 |
| 05:00 PM | 17:00 |
| 06:00 PM | 18:00 |
| 07:00 PM | 19:00 |
| 08:00 PM | 20:00 |
| 09:00 PM | 21:00 |
| 10:00 PM | 22:00 |
| 11:00 PM | 23:00 |
The 24-hour time system that is used throughout the modern world can be traced back to the ancient Egyptians.
Days were divided into 10 sections, which were measured using shadow clocks, water clocks, and various other devices. Although there is some speculation amongst historians, it is believed that the ancient Egyptians were the first to divide days into 24 sections of equal measure.
Each day was divided into two 10-hour parts, with an additional two hours at the beginning and end of each day. The first additional hour was called the 'twilight hour'.
The ancient Egyptians based their nighttime on 36 groups of stars in the sky called 'decans'. These star groups would rise in 40-minute intervals, which is what they based their time on. Tables and information referring to this time process have been discovered inside some sarcophagi (coffins). It is believed that the information was etched on the interior of the sarcophagi so that the dead could tell the time and make sure that they caught the ferry on time, which would transport them to the afterlife.
You can convert time between the 12-hour clock to the 24-hour clock by adding 12 hours onto the time if it proceeds midday. This is because the 24-hour clock consists of two 12-hour segments that follow one another. This method can also be used in reverse order to convert time between the 24-hour clock to the 12-hour clock.
Most English-speaking countries use the 12-hour clock, although the 24-hour clock is frequently used too, especially in terms of public transport. Non-English speaking countries prefer to use the 24-hour clock. However, the time is verbally read in different ways across various countries. English-speaking countries rarely refer to the 24-hour clock when speaking the time, even if they are reading from one. For example, Germans may read three O'clock in the afternoon as 'fünfzehn Uhr', which translates to 'fifteen O'clock' in English. However, an American would read it as '3 PM' or just 'three O'clock'.
A digital 24-hour clock always features four digits - single-figure hours before midday feature a zero in front. The minutes and seconds are the same whether the time is read from a 12-hour or 24-hour clock, as it is only the hours that may change depending on whether the time is after midday or not. Analog clocks are split up into 12 sections, which are further divided into five minutes.
A system called military time uses the 24-hour clock, which also accompanies additional information concerning the timezone the individuals are referring to. The time is verbally read in a set way so that the hours are always referred to in hundreds. For example, 02:00 in military time would be referred to as 'zero two hundred hours', rather than two O'clock.
