10K Time Predictor (Riegel)

Predict 10K via Riegel: T₂ = T₁ × (D₂/D₁)^1.06.

Result

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How to use this calculator

Enter known race distance + time.
Read predicted 10K.

About this calculator

Predict 10K race time from a recent shorter or longer race using Riegel's formula. Most accurate when input race is within 2× distance ratio. 5K → 10K is the most reliable prediction (small extrapolation, similar physiology). Marathon → 10K underestimates 10K time (you have more endurance than speed).

Frequently asked

Best base for 10K prediction?+

5K result, recent. Half-marathon also works.

Why is the exponent > 1?+

Doubling distance doesn't halve speed; you slow somewhat. Empirically ~1.06.

Adjustments for course?+

Hilly course: add 1-3% to predicted time. Trail: 5-10%. Heat above 70°F: 1-2% per 10°F.

Daniels VO2max method?+

Alternative: estimate VDOT, predict from VDOT tables (Jack Daniels Running Formula). Similar accuracy.

Untrained for distance?+

Predicting marathon from a 5K when you've never run >10K: unreliable. Need long-run training base.

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