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The following method is a rough guide to calculating how much time it will take to run a particular distance. This popular method, known as the 4 second rule, gives an idea of the sort of times a runner might achieve in a race. It is useful for anyone whose been following the easy running plan or any plan based on time rather than distance, although the calculation requires at least one measurement of time taken to run a specific distance. To measure a distance on your regular running route use an online route planner.

The 4 second rule works on the basis that as distance increases the runner will have to run more slowly. Each 400m covered adds 4 second to the time so, as an example, if it takes 3 minutes to run 400m the time used for calculations would be 3 minutes 4 seconds.

It can be difficult to find a measured 400m unless you visit the local running track and it may be easier to time a run over a measured mile. Since a mile is around 1600m just divide the time taken to run 1 mile by 4. This gives an approximate base 400m time to use in the calculation.

Running 1 mile in 10 minutes is roughly equivalent to running 400m in 2 minutes 30 seconds. (since 1 mile is approx 1600m and 1600m divided by 4 = 400m). So the base figure for 400m is 2 minutes 30 seconds. To use this to calculate longer distances add 4 seconds to give 2 minutes 34 seconds. Having applied the 4 second rule we can assume every 400m takes 2 minutes 34 seconds to run.

With this example the 5km target would be calculated in the following way: 400m x 12.5 = 5000m (5km). Our 400m time (including the 4 second rule) is 154 seconds or 2 minutes 34 seconds . So 154 seconds x 12.5 = 1925 seconds or 32 minutes 5 seconds. The runner covering one mile in 10 minutes could target 32 minutes 5 seconds for a 5km race.