Runner tool
Race predictor
Estimate equivalent race performances using the Riegel formula. Predictions are guides, not guarantees.
Predicted finish times
Enter a recent result to estimate equivalent performances.
How it works
Predictions use the Riegel formula: predicted time = reference time × (target distance ÷ reference distance) raised to the power of 1.06. The exponent is an empirical constant that reflects how average pace slows as race distance grows.
Frequently asked questions
What is a race equivalency calculator?
It estimates how a recent result at one distance compares to a different distance, so a 5K personal best can be used to estimate a 10K, half marathon, or marathon time.
What is the Riegel formula?
Riegel's formula predicts a finish time as T2 = T1 × (D2 ÷ D1) raised to the power 1.06, where T1 is your known time, D1 the known distance, and D2 the target distance.
How accurate are race time predictions?
They are estimates based on a single recent result and assume similar training, terrain, and conditions. Treat predictions as guides rather than guaranteed times.