close this window.
Skillswise Factsheet
MSS1/L1.2

12 and 24 hour times

8:27

Look at the clock above. How can you tell if it's morning or evening? You can't!
12 hour digital clocks usually have a way of showing if it is a.m. or p.m., but it's much easier to tell on a 24 hour digital clock.

20:27

From this clock we can tell it's evening, but how do we know what the hour is, as we're used to using the numbers 1-12?
The clock says 20 hours and 27 minutes. To change this time to the 12 hour clock take away 12 from the hours
      20 - 12 = 8
So we know that it's something past 8 at night. The number after the colon (:) gives us the minutes. So it's 27 minutes past 8.
So 20:27 is the same as 8:27 p.m.

Example What is 17.42 in the 12 hour clock?

Again start by taking 12 from the hours
      17 - 12 = 5
So 17.42 is the same as 5.42 p.m. which is 42 minutes past 5 in the evening.

It's useful to know this time as 'so many minutes' to 6 as well, so how do we work out the minutes before 6?
Take the minutes away from 60, as there are 60 minutes in 1 hour
      60 - 42 = 18
so it's 18 minutes to 6 in the evening.

18 minutes to six o'clock

What about converting a time into the 24 hour system?
For example what is 3.36 p.m. in the 24 hour clock?

This time is p.m. so add 12 onto the hours (the number in front of the point)
      3 + 12 = 15
so 3.36 p.m. will be 15.36 in the 24 hour clock.

Feeling confident about converting from 12hr times to 24hr times and vice versa? Why not try Worksheet 2?


You can find Skillswise at http://www.bbc.co.uk/skillswise
This factsheet is BBC Copyright