Race Time Predictor
Free calculator·Instant results
Marathon (Riegel)
3:40:49
- Marathon (VDOT)
- 3:40:41
- Half (Riegel)
- 1:45:54
- VDOT
- 42
| Race | Riegel | VDOT | VDOT pace /mi |
|---|---|---|---|
| Mile | 6:55 | 6:49 | 6:49/mi |
| 5K | 23:01 | 23:08 | 7:27/mi |
| 10K | 48:00 | 48:00 | 7:43/mi |
| Half marathon | 1:45:54 | 1:46:25 | 8:07/mi |
| Marathon | 3:40:49 | 3:40:41 | 8:25/mi |
The numbers
How it works
This race time predictor gives two predictions for every distance. Riegel's formula, T2 = T1 × (D2 ÷ D1)^1.06, projects the example 48:00 10K to a 3:40:49 marathon and a 1:45:54 half.
The VDOT column (42) is usually a little more optimistic for the marathon — 3:40:41 here — and assumes marathon-specific training. Raise the Riegel exponent to 1.08 if your mileage is low.
Questions
FAQ
How accurate are race time predictors?
Within a few percent up to the half; marathon predictions assume full marathon training.
What exponent should I use?
1.06 is Riegel's original; 1.07–1.08 suits runners with less endurance than speed.
Why do Riegel and VDOT differ?
They model fatigue differently: 3:40:49 vs 3:40:41 for the example.
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