Working With The 24 Hour Clock System


Hi there. In this education post, I will cover the 24 hour clock system. It is assumed that the student is comfortable with addition, subtraction and telling time in the 12 hour clock system from an analog clock.

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  • The 24 Hour Clock
  • Elapsed Time
  • Some Exercises With Solutions


The 24 Hour Clock

For those who are very comfortable with the 12 hour clock system, using the 24 hour time system can be confusing. The brain does have to adjust to the 24 hour system.

Times in the 24 hour system is referred as either military time or continental time. Twenty-four hour time systems are used in the military, transportation, computers and in timetables. According to the Military Time website many European, Latin American and Asian nations adopt the 24 hour time system.

The start of the day start at midnight with the time of 00:00 in the 24 hour system. This time corresponds to 12:00 AM in the 12 hour clock system. There is no AM or PM in the 24 hour system.

A time of 08:00 in the 24 hour system is the same as 8:00 AM in the 24 hour system.

Noon is 12:00PM in the 12 hour time system. In the 24 hour system it is expressed as 12:00.

Time in the afternoon start to past the 12 hour mark of the day until hitting 24:00. A time such as 2PM would be 14:00 in the 24 hour system. This is 2 hours past noon (12 + 2).

An evening time such as 8:00PM is 20:00. This is 8 hours past 12PM.

Summary Table

Time In 12 Hour SystemTime In 24 Hour System
12:00 AM00:00
8:00 AM08:00
12:00 PM12:00
2:00 PM14:00
8:00 PM20:00
10:00 PM22:00


An Interactive Clock Website

This neat interactive clock from ToyTheater allows for playing with an analog clock. The default mode is on the 12 hour system but you can change it to the 24 hour time system.



Elapsed Time

Elapsed time refers to amount of time that has passed from a start time to another time. In other words, elapsed time represents how long from a start time to a finish time.

Example One

How many hours are there between 02:00 and 12:00?

This one is quite simple. Going from 02:00 to 12:00 is 10 hours.


Example Two - Crossing Over Noon

How many hours have elapsed from 11:00 to 15:00?

The answer here is 4 hours. Computing this answer is easier in the 24 hour format than in the 12 hour format. The times in the 12 hour format are 11:00AM and 3PM. You would have to remember that after 12:00PM the clock goes from 12 to 1 to 2 and so on in the 12 hour format.


Example Three - Crossing Over Midnight

Determine the number of hours elapsed between the times of 22:00 and 5:00.

There are two hours from 22:00 to 24:00. From 24:00 to 5:00 this would be 5 hours. Combine 2 hours and 5 hours to obtain the answer of 7 hours.


Example Four - Hours and Minutes

What is the elapsed time from 20:35 to 2:25?

When it comes to hours and minutes I like to break it down into sections.

It is 25 minutes from 20:35 to 21:00.

There are 3 hours from 21:00 to 2:00.

From 2:00 to 2:25 would be 25 minutes.

Adding all these pieces together yields an answer of 3 hours and 50 minutes.


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Some Exercises With Solutions

Question One

How many hours are there between 7:00 and 16:00?


Question Two

Mario works a night shift from 22:00 to 6:00. How many hours does Mario work in this night shift?


Question Three

What is the elapsed time from 7:30 to 14:25?



  1. 9 hours from 7:00 to 16:00

  2. Mario's night shift lasts 8 hours.

  3. 6 Hours and 55 minutes.

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Thank you for reading.