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Race converter5 km to half marathon time converter
Your half marathon prediction is roughly 4.60× your 5 km (parkrun) time: a 26:00 points to about 1:59:42, if you train for the longer race. parkrun to half marathon is the step most runners take next, and the conversion is reliable enough to plan on if you build the long run to 16–18 km.
| Distance | Predicted time | Pace |
|---|---|---|
| 5 km | 26:00 | 5:12/km |
| 10 km | 53:59 | 5:24/km |
| 15 km | 1:23:11 | 5:33/km |
| Half marathon | 1:59:42 | 5:40/km |
| Marathon | 4:07:08 | 5:51/km |
| Two Oceans 56 km * | 5:51:03 | 6:16/km |
| Comrades (about 90 km) * | 10:32:14 | 7:01/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
| 5 km (parkrun) | Half marathon (VDOT) | Riegel | Pace |
|---|---|---|---|
| 18:00 | 1:22:33 | 1:22:48 | 3:55/km |
| 20:00 | 1:31:50 | 1:32:00 | 4:21/km |
| 22:00 | 1:41:07 | 1:41:12 | 4:48/km |
| 24:00 | 1:50:25 | 1:50:24 | 5:14/km |
| 25:00 | 1:55:03 | 1:55:00 | 5:27/km |
| 26:00 | 1:59:42 | 1:59:36 | 5:40/km |
| 28:00 | 2:08:57 | 2:08:48 | 6:07/km |
| 30:00 | 2:18:09 | 2:18:00 | 6:33/km |
| 32:00 | 2:27:19 | 2:27:12 | 6:59/km |
| 35:00 | 2:40:58 | 2:41:00 | 7:38/km |
| 38:00 | 2:54:30 | 2:54:48 | 8:16/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 26:00 5 km (parkrun) they give 1:59:42 and 1:59:36. 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 half is four times longer than a parkrun, so endurance starts to matter as much as speed. The prediction holds for runners who build the weekly long run steadily; without it, the last 5 km give the time back.
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 5 km (parkrun) time to a half marathon time?
Multiply by about 4.60, or use the chart: a 26:00 points to about 1:59:42.
What half marathon can I run off a 20:00 5 km (parkrun)?
About 1:31:50 by Daniels’ model, 1:32:00 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?
The half is four times longer than a parkrun, so endurance starts to matter as much as speed. The prediction holds for runners who build the weekly long run steadily; without it, the last 5 km give the time back.