Race time predictor
Enter a recent time over one distance: we estimate what it’s worth over the others.
Reference race
Your time
hmins
| Distance | Predicted time | Pace |
|---|---|---|
| 5K | 23:59 | 4'48 min/km12.5 km/h |
| 10K(your race) | 50:00 | 5'00 min/km12 km/h |
| Half marathon | 1:50:19 | 5'14 min/km11.5 km/h |
| Marathon | 3:50:01 | 5'27 min/km11 km/h |
Equivalent times from a 10K
| 5K | 10K | Half marathon | Marathon |
|---|---|---|---|
| 19:11 | 40:00 | 1:28:15 | 3:04:00 |
| 21:35 | 45:00 | 1:39:17 | 3:27:01 |
| 23:59 | 50:00 | 1:50:19 | 3:50:01 |
| 26:23 | 55:00 | 2:01:21 | 4:13:01 |
| 28:47 | 1:00:00 | 2:12:23 | 4:36:01 |
| 31:11 | 1:05:00 | 2:23:25 | 4:59:01 |
| 33:34 | 1:10:00 | 2:34:27 | 5:22:01 |
Riegel’s formula
Published by engineer Peter Riegel in 1977, it estimates a time T2 over a distance D2 from a time T1 over a distance D1: T2 = T1 × (D2 ÷ D1)^1.06.
The 1.06 exponent accounts for fatigue: when the distance doubles, the time a little more than doubles.
Limits of the prediction
- It assumes training suited to the target distance: without long runs, your marathon will be slower than predicted.
- It is more reliable between close distances (5K to 10K) than between a 5K and a marathon.
- The course, the weather and how you feel on the day matter as much as the maths.
Frequently asked questions
Is my predicted marathon time realistic?
It’s the time of a runner well trained for the marathon. Without several months of long runs, expect 5 to 10% more.
Which race time should I use?
A recent one (less than two months old), run all out on a flat course. A 10K or a half marathon give the most reliable estimates.
What is a 45-minute 10K worth over a half and a full marathon?
About 1:39 for a half marathon and 3:27 for a marathon, according to Riegel’s formula.