Riegel Race Time Predictor

Predicting performance across distances

Peter Riegel's 1977 formula predicts race time at a new distance from a known result at another distance, using an exponent (1.06) reflecting that runners inevitably slow down somewhat per unit distance as races get longer.

Worked example

For a 25-minute 5K, predicting a 10K time:

T2 = 25 x (10/5)^1.06 = 0h 52m (52.12 total minutes)

Frequently asked questions

Why isn't the predicted 10K time simply double the 5K time? If pace stayed exactly constant, doubling distance would double time - but the 1.06 exponent captures the real-world tendency for sustainable pace to slow slightly at longer distances, which is why the predicted time (52.1 minutes) is a bit more than exactly double the 5K time (50 minutes).

How accurate is this prediction? It works best when predicting between similar distance ranges (5K to 10K, for example) with comparable training - predictions across very different distance ranges (like 5K to marathon) are less reliable, since they involve different physiological demands (aerobic capacity versus fueling and pacing endurance).