Type a time like 50:00 or 1:45:00.
Equivalent times
- 5K
- –
- 10K
- –
- Half marathon
- –
- Marathon
- –
Marathon training paces, per km
- Marathon pace
- –
- Easy
- –
- Threshold
- –
- VMA
- –
How the prediction works
The predictor uses Riegel’s formula, published by the engineer Peter Riegel in 1977 and still the basis of most race calculators: time at a new distance equals your time multiplied by the ratio of the distances to the power 1.06. It is the same model Run 42 uses to turn your goal into training paces.
It works best between similar distances and for runners trained for the target race. From a 10K to a marathon it is optimistic for many people: the marathon depends on endurance and fuelling that a 10K doesn’t test. Treat the result as the ceiling of what your current speed allows, and add a few minutes if your long runs are still short.
10K to marathon conversion
The same formula, as a table:
| 10K | 5K | Half marathon | Marathon |
|---|---|---|---|
| 35:00 | 16:47 | 1:17:13 | 2:41:00 |
| 40:00 | 19:11 | 1:28:15 | 3:04:00 |
| 45:00 | 21:35 | 1:39:17 | 3:27:01 |
| 50:00 | 23:59 | 1:50:19 | 3:50:01 |
| 55:00 | 26:23 | 2:01:21 | 4:13:01 |
| 1:00:00 | 28:47 | 2:12:23 | 4:36:01 |
| 1:05:00 | 31:11 | 2:23:25 | 4:59:01 |
| 1:10:00 | 33:34 | 2:34:27 | 5:22:01 |
| 1:15:00 | 35:58 | 2:45:29 | 5:45:01 |
From prediction to goal
A good marathon goal sits between the prediction and what your long runs tell you. Once you have it, the marathon pace chart gives every pace you need, and the sample plans for sub-3:30, sub-4 and sub-4:30 show how a full block is built.
