Race Time Predictor
Estimate your times at every distance from a known result — Riegel's formula.
🏃 Your result
10K — 00:50:00
How does it work?
The predictor uses Riegel's formula (T₂ = T₁ × (D₂/D₁)^1.06), a recognized mathematical model that estimates race time at a target distance from a known result. The closer the reference distance is to the target, the more reliable the prediction.
Equivalent performances
| Distance | Time | Pace (min/mi) | Speed (mph) |
|---|---|---|---|
| 1 Mile | 7:13 | 7:13 | 8.32 |
| 5K | 23:59 | 7:43 | 7.77 |
| 10K | 50:00 | 8:03 | 7.46 |
| 15K | 1:16:51 | 8:15 | 7.28 |
| Half Marathon | 1:50:19 | 8:25 | 7.13 |
| Marathon | 3:50:01 | 8:46 | 6.84 |
| 50K | 4:35:21 | 8:52 | 6.77 |
| 100K | 9:34:05 | 9:14 | 6.49 |
Frequently asked questions
How does Riegel's formula work?
Riegel's formula (T₂ = T₁ × (D₂/D₁)^1.06) is a mathematical model published in 1977 by Peter Riegel. It's based on the principle that race time increases non-linearly with distance: the longer the distance, the slower the pace due to fatigue. The 1.06 exponent reflects the average fatigue factor observed in runners.
How reliable is the race time predictor?
The prediction is more reliable when the reference distance is close to the target distance. For example, a 10K time predicts a half marathon well, but is less accurate for a 100K. The formula also assumes proper training for the target distance — a 5K runner who has never run more than 10K will likely be slower than predicted for a marathon.
Can I use a training time as a reference?
Ideally, use a recent official race time (within the last 3 months). A training time may underestimate your abilities (without race-day adrenaline) or overestimate them (if conditions were ideal). However, a timed track test can provide a good approximation.
Why are ultra-distance predictions less accurate?
Beyond the marathon, other factors come into play: race nutrition, time spent at aid stations, elevation, sleep management for ultra-trails. Riegel's formula is optimized for road distances from 1,500m to 42K. For ultras, consider the predictions as a rough estimate.