Race Equivalent Performance Calculator

About this calculator

The Riegel formula, published by exercise scientist Peter Riegel in 1977, predicts an equivalent race time at a different distance from a known performance: T2 = T1 × (D2 ÷ D1)^1.06, where the exponent of 1.06 captures the fact that pace naturally slows as race distance increases (fatigue accumulates faster than distance alone would suggest). A runner's 5K time can, for example, be used to predict an equivalent marathon time using this scaling relationship.

Coaches and runners use race-equivalent calculations to set realistic goal times for an upcoming race based on a recent result at a different distance, to gauge whether current fitness supports a target time, and to compare performances across events like the widely referenced age-graded and Riegel-based scoring tables used in road racing.

This calculator takes a known race time and distance along with a target distance and returns the Riegel-predicted equivalent time, useful for setting pacing goals when transitioning between distances such as 10K to half-marathon or half-marathon to marathon.