Race time predictor

Predict a 5K/10K/half/marathon time from a recent race using the Riegel formula.

Calculated in this browser. Nothing is sent anywhere.

Riegel formula (T2 = T1 × (D2/D1)^1.06) — same-fitness, same-conditions estimate. Distance 0.1–500 km.

How to use

  1. Enter the distance and your finish time.
  2. Pick a target distance and read the prediction and required pace.

What it supports

Riegel exponent 1.06, input distances 0.1–500 km, finish times 60 s–48 h. A prediction, not a training plan — heat, course, and training all move the real number.

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