The 24-hour clock

What is the 24-hour clock?

The 24-hour clock is literally what the name depicts i.e. it runs for 24 hours, unlike the 12-hour clock which runs for two 12 hour lengths.

Since we know that there are 24 hours in one day and it's a 24-hour clock, it makes sense that the 24-hour clock will run for one 24 hour session starting and ending at midnight. The 24-hour clock starts at 00:00 and ends at 23:59. There are no AMs or PMs involved! Some people prefer the following display: 00h00 and 23h59 - both are correct.

Example

What is the time on the above clock? (Note: remember that the long clock hand refers to the minutes, the short hand to the hours and the very thin long hand refers to the seconds. Not all clocks will have a second hand.)

Using the 12-hour clock do you agree that the time could read either:

• 10.10am
• OR
• 10.10pm

We would only know whether it's am or pm by whether it is light or dark outside!

Using the 24-hour clock we will tell the above time as follows:

• 10h10 if it was in the morning 
• OR
• 22h10 if it was during the night

Do you see where we got the 22 from? 10 o'clock at night is the 22nd hour after midnight.

Watch the YouTube video below which clearly describes the 24-hour clock.

Welch, A. (2015). The 24-hour clock (Standard YouTube licence)

Now that you have a better understanding of the differences between the 12-hour and 24-hour clocks, complete the quiz below where you should answer the questions requesting you to convert the times from one clock to another!