Running
Race Time Predictor
Predict your time at a new distance from a recent result using Riegel's endurance model.
Free · instant · no sign-upDeterministic
Result
Predicted time52:07
Over 10 km at even effort.
Predicted pace5:13/ km
Riegel's model assumes even pacing and comparable conditions; longer extrapolations are less reliable.
The formula
Riegel's formula
T₂ = T₁ × (D₂ ÷ D₁)^1.06
Source: Peter Riegel, "Athletic Records and Human Endurance" (1981)
The 1.06 fatigue exponent is Riegel’s published value.
What it means
- A well-known model for how endurance times scale with distance.
- Works best when the two distances are reasonably close and both raced at full effort.
Limitations
- Assumes matching training, pacing and conditions.
- Extrapolating from a 1500 m to a marathon is unreliable — the further you extrapolate, the softer the estimate.
Educational only
This is a deterministic tool: the same inputs always give the same result. It is for learning and planning, not a substitute for coaching or measurement.
Keep exploring
Follow the threads from this tool into the wider knowledge base.