Running pace calculator
Give any two of pace, time and distance, and the third follows. Equivalent times for the standard race distances come with it, using the prediction formula coaches have relied on since 1977.
- Time
- 50:00
- Distance
- 10 mi
- Speed in km/h
- 19.31
- Speed in mph
- 12.00
- Per kilometre
- 3:06
- Per mile
- 5:00
- Per 400 m lap
- 1:15
| Distance | Predicted time | Predicted pace |
|---|---|---|
| race:5k | 14:29 | 4:40 |
| race:10k | 30:12 | 4:52 |
| race:half | 1:06:37 | 5:05 |
| race:marathon | 2:18:54 | 5:18 |
The formula
Pace = time / distance, and its two rearrangements. Equivalent race times use Riegel's formula, t₂ = t₁ · (d₂/d₁)^1.06, which holds reasonably for distances within a factor of about three.
Worked example
10 km in 50 minutes is a pace of 5:00 per kilometre, or 12 km/h. Riegel predicts about 24:07 for 5 km and 1:52:14 for a half marathon.
How to use it
- 1Switch the unit to whatever your watch shows — mixing kilometre pace with mile splits is the usual source of confusion.
- 2Use a recent race or hard time trial as the input, not a training average, if you want a realistic prediction.
- 3Treat the marathon prediction with suspicion unless you have done the long runs. The formula assumes the endurance base is there.
Questions people ask
Why is my predicted marathon time optimistic?
Because Riegel's formula assumes you are trained for the distance. Extrapolating from 5 km to a marathon stretches it well beyond the range where it holds, and fuelling and muscular fatigue dominate the last ten kilometres.
Does the exponent change?
Yes. 1.06 is the original figure for trained runners; 1.07 to 1.10 fits recreational runners better over long distances. Treat the predictions as the optimistic end of a range.
Last reviewed: 2026-10-20