Predict a race time at one distance from a result at another.
Riegel’s formula raises the distance ratio to a power slightly above one, which captures the pace degradation over longer races. It is accurate within about two per cent for distances within a factor of four. Predicting a marathon from a 5K stretches the formula beyond its reliable range, because marathon performance depends on endurance training the shorter race never tests.
Race Predictor
Riegel formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06
These figures are estimates based on population-average formulas and are intended for training and recreational planning only. They are not medical advice. Consult a qualified health professional before starting or changing an exercise programme, particularly if you have an existing medical condition.
Riegel formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06 Riegel’s formula raises the distance ratio to a power slightly above one, which captures the pace degradation over longer races. It is accurate within about two per cent for distances within a factor of four.
Predicting a marathon from a 5K stretches the formula beyond its reliable range, because marathon performance depends on endurance training the shorter race never tests.
This calculator takes 4 inputs: Known race distance, Known race time, Target race distance, Fatigue exponent. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.