12-hour and 24-hour clock

Time is measured using either the \(12\)-hour clock or the \(24\)-hour clock.

12-hour clock

The \(12\)-hour clock notation uses am and pm to indicate morning and afternoon.

  • \({am}\) is the time from \(12\) midnight and before \(12\) noon (\(12.00pm\) is midday)
  • \({pm}\) is the time from \(12\) midday and before \(12\) midnight (\(12.00am\) is midnight)

For example

  • \[6.23am\]
  • \[7.45pm\]

24-hour clock

The \(24\)-hour clock does not require the use of am or pm. Afternoon is indicated by a number bigger than \(12\).

curriculum-key-fact
When converting from the 12-hour clock to the 24-hour clock remember: for any time after 12.59pm, add 12 to the hours.

For example

  • \(6.23pm\) becomes \((6.23 + 12) = \text{18:23}\)
  • \(7.45pm\) becomes \((7.45 + 12) = \text{19:45}\)

The \(24\)-hour clock always uses \(4\) digits, so for any time before \(\text{10:00}\) a zero is placed at the beginning.

For example

  • \(\text{01:00}\) means \(1.00am\)
  • \(\text{13:00}\) means \(1.00pm\)
  • \(\text{04:00}\) means \(4.00am\)
  • \(\text{16:00}\) means \(4.00pm\)
Question

Copy and complete the following table, then check your answers.

Table to convert times in the 12-hour clock and 24-hour clock format
Completed table showing times in the 12-hour clock and 24-hour clock format