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Race converter10 km to marathon time converter
Your marathon prediction is roughly 4.58× your 10 km time: a 52:00 points to about 3:58:25, if you train for the longer race. A 10 km gives a sound marathon estimate for runners who have done the long runs — and a flattering one for those who have not.
| 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 | Marathon (VDOT) | Riegel | Pace |
|---|---|---|---|
| 38:00 | 2:55:29 | 2:54:48 | 4:10/km |
| 42:00 | 3:13:43 | 3:13:13 | 4:35/km |
| 45:00 | 3:27:15 | 3:27:01 | 4:55/km |
| 48:00 | 3:40:41 | 3:40:49 | 5:14/km |
| 50:00 | 3:49:34 | 3:50:01 | 5:26/km |
| 52:00 | 3:58:25 | 3:59:13 | 5:39/km |
| 55:00 | 4:11:36 | 4:13:01 | 5:58/km |
| 58:00 | 4:24:41 | 4:26:49 | 6:16/km |
| 1:00:00 | 4:33:22 | 4:36:01 | 6:29/km |
| 1:05:00 | 4:54:54 | 4:59:01 | 6:59/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 3:58:25 and 3:59:13. 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
The marathon prediction assumes a full block: long runs past 30 km, weekly mileage that suits the goal, and race-day fuelling practised in training. Miss those and the last 10 km decide the time.
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.
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Common questions
How do I convert a 10 km time to a marathon time?
Multiply by about 4.58, or use the chart: a 52:00 points to about 3:58:25.
What marathon can I run off a 42:00 10 km?
About 3:13:43 by Daniels’ model, 3:13:13 by Riegel’s, if you train for the 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 marathon?
The marathon prediction assumes a full block: long runs past 30 km, weekly mileage that suits the goal, and race-day fuelling practised in training. Miss those and the last 10 km decide the time.