Race Shape › Calculators › Race time predictor › 10 km to half marathon time converter
Race converter10 km to half marathon time converter
Your half marathon prediction is roughly 2.22× your 10 km time: a 52:00 points to about 1:55:18, if you train for the longer race. A 10 km is the best single predictor of a half marathon: close enough in length that the same fitness carries across.
| Distance | Predicted time | Pace |
|---|---|---|
| 5 km | 25:03 | 5:01/km |
| 10 km | 52:00 | 5:12/km |
| 15 km | 1:20:07 | 5:20/km |
| Half marathon | 1:55:18 | 5:28/km |
| Marathon | 3:58:25 | 5:39/km |
| Two Oceans 56 km * | 5:38:39 | 6:03/km |
| Comrades (about 90 km) * | 10:09:54 | 6:47/km |
Flat course, good conditions, properly trained for the distance. * Past the marathon, times follow how real Two Oceans and Comrades fields finish (about 1.42× and 2.56× a marathon), not the pure fitness model.
The chart
| 10 km | Half marathon (VDOT) | Riegel | Pace |
|---|---|---|---|
| 38:00 | 1:24:04 | 1:23:50 | 3:59/km |
| 42:00 | 1:33:02 | 1:32:40 | 4:25/km |
| 45:00 | 1:39:44 | 1:39:17 | 4:44/km |
| 48:00 | 1:46:25 | 1:45:54 | 5:03/km |
| 50:00 | 1:50:52 | 1:50:19 | 5:15/km |
| 52:00 | 1:55:18 | 1:54:44 | 5:28/km |
| 55:00 | 2:01:56 | 2:01:21 | 5:47/km |
| 58:00 | 2:08:33 | 2:07:58 | 6:06/km |
| 1:00:00 | 2:12:56 | 2:12:23 | 6:18/km |
| 1:05:00 | 2:23:52 | 2:23:25 | 6:49/km |
| 1:10:00 | 2:34:44 | 2:34:27 | 7:20/km |
Two formulas, one answer
The VDOT column is Jack Daniels’ model, the same one that sets every Race Shape plan. The Riegel column is Pete Riegel’s 1977 formula, T₂ = T₁ × (D₂/D₁)^1.06, which most online calculators use. For a 52:00 10 km they give 1:55:18 and 1:54:44. When two independent models agree to within a few minutes, the estimate is about as good as a formula gets.
When the prediction is wrong
Most trained runners land within a minute or two of the prediction. If you come in well slower, the long run was too short or the first 5 km too quick.
At altitude, add the correction on top: a race at Johannesburg’s height is about 8% slower for the same effort — see the altitude pace calculator.
Build my half marathon plan — free to buildSee your whole block before you pay.
Common questions
How do I convert a 10 km time to a half marathon time?
Multiply by about 2.22, or use the chart: a 52:00 points to about 1:55:18.
What half marathon can I run off a 42:00 10 km?
About 1:33:02 by Daniels’ model, 1:32:40 by Riegel’s, if you train for the half marathon.
Which is more accurate, VDOT or Riegel?
They agree closely over these distances. VDOT is slightly more conservative for slower runners; neither knows how much long-run training you have done, which matters more than the formula.
Why did I run slower than my predicted half marathon?
Most trained runners land within a minute or two of the prediction. If you come in well slower, the long run was too short or the first 5 km too quick.