5K Time Predictor (Riegel)
Predict 5K from another race using Riegel formula: T₂ = T₁ × (D₂/D₁)^1.06.
Result
Predicted 5K time
22:51
Pace: 7:21/mi.
- Known distance13.1 mi
- Known time105:00
- Predicted 5K22:51
- Predicted pace7:21/mi
Step-by-step
- Riegel: T₂ = T₁ × (D₂/D₁)^1.06.
- T₂ = 6300s × (3.107/13.1)^1.06 = 1,371s.
How to use this calculator
- Enter recent race: distance + time.
- Predicted 5K appears.
About this calculator
Riegel's race-time formula (Pete Riegel, 1981): T₂ = T₁ × (D₂/D₁)^1.06. The 1.06 exponent reflects fatigue at longer distances. Most accurate within 2-3× distance ratio. Less accurate predicting marathon from 5K (extrapolation too far) — use long-tempo training pace as input for marathon predictions instead. Useful for setting realistic 5K goals after a recent half-marathon.
Frequently asked
Riegel's empirical fit. Reflects fatigue accumulation. Some athletes use 1.04 (faster fade), 1.08 (slower).
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