Race Time Predictor (Riegel formula)
Predict your time at any distance using Riegel's formula T₂ = T₁ × (D₂/D₁)^1.06.
Result
Predicted time
3:50:01
Riegel T₂ = T₁ × (D₂/D₁)^1.06.
- Base race10.00 km in 50:00
- Target42.195 km
- Ratio(42.195 / 10.00) = 4.2195
- Multiplier4.2195^1.06 = 4.6002
Step-by-step
- Convert both distances to km: 10.000 km → 42.195 km.
- Compute the ratio raised to the exponent: (42.195/10.000)^1.06 = 4.6002.
- Multiply by base time: 3000 × 4.6002 = 13,801 s.
How to use this calculator
- Enter a recent race distance and time.
- Enter the target distance.
- Optionally bump the exponent to 1.07-1.08 for big distance jumps.
About this calculator
Peter Riegel published the formula T₂ = T₁ × (D₂/D₁)^1.06 in 1981. The exponent 1.06 captures the empirical fact that runners slow down slightly as race distance increases. The formula works best within 2× of your base distance and tends to under-predict the marathon if your base is a 5K or 10K (because long-run-specific endurance matters). Some sources recommend 1.07 or even 1.08 for distances above the half.
Frequently asked
Riegel fitted the exponent to thousands of road-race results. It minimizes prediction error across distances from 1500 m to the marathon for trained runners.
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