Predict a half marathon from a 50-minute 10K
By Jesús Narváez Tamés ·
Riegel equivalence: what half marathon lines up with a 50:00 10K if you actually train for the distance.
1:50:19Half marathon
- Known result
- 10 km in 50:00
- Known pace
- 5:00 min/km
- Target distance
- Half marathon
Start from a 10K in 50:00, which is 5:00 per kilometre. Riegel stretches that mark to the half marathon with the 1.06 exponent. The time above is an equivalence, not a race-day promise.
It comes out optimistic if your long run is still 10 km. The formula assumes you have trained the new distance. Without that, add a few minutes, and do not lock the pace on race morning just because the number fits.
How this was calculated
Riegel (1981): T2 = T1 × (D2/D1)^1.06. Useful as a ballpark from 5K to the marathon when you train for the distance. At marathon distance it tends to be optimistic.
Nearby values
The same calculation changing only the time. The highlighted row is this example.
| Time | Result |
|---|---|
| 48:00 | 1:45:54 Half marathon |
| 49:00 | 1:48:07 Half marathon |
| 50:00 | 1:50:19 Half marathon |
| 51:00 | 1:52:32 Half marathon |
| 52:00 | 1:54:44 Half marathon |
Adjust it to your numbers
The calculator starts from this example. If you change a field, that value is saved only on this device.
Prediction (Riegel formula)
- 1 km4:217:01/mi
- 5 km23:597:43/mi
- 10 km50:008:03/micurrent
- Half marathon1:50:198:25/mi
- Marathon3:50:018:46/mi
The Riegel formula assumes adequate training for the target distance. For marathons it tends to overestimate.
Open the calculator without this example
Frequently asked questions
What half marathon equals a 50-minute 10K?+
From a 10 km in 50:00, Riegel estimates Half marathon in 1:50:19. Only if you train the distance. On a 10K endurance base, race day will be slower.
Can the same sum be used for a marathon?+
From a 10 km in 50:00, Riegel estimates Half marathon in 1:50:19. You can, and it usually comes out too fast. At marathon distance Riegel is optimistic: add a margin.
Worked examples
A specific profile, with the number already done. Open it if it looks like you, then adjust.