Running Pace Calculator

Enter any two of distance, time and pace, and get the third — plus the splits you would need to hit for every standard race distance.

The conversions

The only subtlety is that pace and speed move in opposite directions: a lower pace is faster, while a higher speed is faster. Treadmills display speed, most running watches display pace, and mixing the two up is a common source of confusion when following a plan.

Note that the marathon is 42.195 km, not 42. Those 195 metres add roughly 55 seconds at a 4:40/km pace — enough to matter if you are chasing a round-number target.

Pacing a race

Even pacing is very close to optimal for distances from 5 km upwards. Almost every world record at these distances has been set with a slightly negative split — the second half marginally faster than the first.

The classic amateur error is the opposite. Going out 10 seconds per kilometre too fast in the first few kilometres feels almost free, because you are fresh and the effort is buffered. The cost arrives later and is not proportional: the time lost in the closing stages typically exceeds the time gained early by a factor of two or three.

A practical rule for a marathon: run the first 5 km about 5–10 seconds per kilometre slower than goal pace, settle into goal pace through the middle, and spend whatever is left after 30 km.

Predicting across distances

Riegel's formula estimates a time at one distance from a known time at another:

The 1.06 exponent reflects the fact that pace degrades as distance grows. It works well between comparable distances — predicting a 10 km from a 5 km, say — and becomes optimistic when extrapolating from short races to the marathon, where fuelling, heat and muscular durability dominate in a way that pure aerobic capacity does not capture.

A commonly cited sanity check for the marathon is double your half marathon time and add 10–20 minutes. If a Riegel prediction from your 5 km suggests much faster than that, believe the half marathon.