Riegel Formula Calculator — Race Time Prediction
Use the Riegel formula to predict race times for any distance from a known result.
1.06 for road, 1.07-1.08 for trail/ultra
How We Calculate This
The Riegel Formula
T2 = T1 × (D2 / D1)^exponent
Where T1 = known time, D1 = known distance, D2 = target distance, and exponent = fatigue factor (default 1.06).
The formula was derived from analysis of world records and accounts for the non-linear relationship between distance and performance.
Frequently Asked Questions
Related Calculators
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10K Predictor
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5K Predictor
Predict your 5K time from shorter or longer race results.
Parkrun Predictor
Predict your parkrun time from other race distances.
Last updated: February 2026
All calculations are estimates. Always consult a coach or medical professional for personalised training advice.