Running pace calculator
Work out the pace a goal time needs — or predict what you could run at another distance from a race you've already done. Plain maths, shown honestly.
Distance
Goal time
Even splits
A race you've run recently
Your time
Predictions use Peter Riegel's endurance formula — the running-world standard for equivalent times. It assumes decent endurance and honest training for the longer distances; a fresh marathon estimate from a 5K is optimistic until you've done the long runs. A projection, not a promise — which is exactly the problem Faster was built to fix: it refines your race forecast from every run you actually do, not one result.
What pace does your goal need?
A quick reference for common goals, at even pace across the whole distance. The calculator above does any time and distance, in kilometres or miles — this is the back-of-the-envelope version.
| Goal | Per km | Per mile |
|---|---|---|
| Sub-20 5K | 4:00 | 6:26 |
| Sub-25 5K | 5:00 | 8:03 |
| Sub-45 10K | 4:30 | 7:14 |
| Sub-50 10K | 5:00 | 8:03 |
| Sub-1:45 half marathon | 4:59 | 8:01 |
| Sub-2:00 half marathon | 5:41 | 9:09 |
| Sub-3:30 marathon | 4:59 | 8:01 |
| Sub-4:00 marathon | 5:41 | 9:09 |
How the race predictor works
Enter a recent race and the tool projects equivalent times at the other standard distances using Riegel's formula: predicted time = known time × (new distance ÷ known distance)1.06. The exponent 1.06 captures how pace fades as distance grows — you can't hold 5K pace for a marathon, and the maths knows it.
The honest caveat every predictor should print and most don't: a prediction is only as good as the training under it. Your equivalent marathon time assumes you've built the endurance to run it — the long runs, the weeks on your feet. Predictors read one performance; coaches read the whole block. That gap is the whole reason plans need to adapt.
Pace, honestly
Most days shouldn't be run at goal pace at all. The fastest way to a faster race is a pile of easy kilometres and a handful of hard ones, run on the right days — which is a harder question than pace, and the one worth asking each morning: should you even run today?