Predict your time for a target distance based on a known race result — using the Riegel formula.
The Riegel formula predicts race times by scaling a known result: T₂ = T₁ × (D₂/D₁)^1.06. The exponent 1.06 accounts for the fact that pace slows as distance increases — you cannot simply double your 5K time to get your 10K time.
The formula works best for distances between 1,500 m and marathon, and for runners who have trained appropriately for both distances. It underestimates ultra-marathon times and overestimates sprint times.
Practical use: if you ran 5K in 25:00, the formula predicts 10K in 51:50 and a half marathon in 1:55. These are not guarantees — they assume equal training, weather and course conditions.
T₂ = T₁ × (D₂/D₁)^1.06 (Riegel, 1977).
Within 2-3% for trained runners over standard distances. It is less accurate for untrained runners or distances outside 1.5-42 km.
It reflects the metabolic cost of endurance: longer distances require more aerobic efficiency and slow the pace. Peter Riegel derived it from world record data.
The formula underestimates ultra times significantly. Ultras involve walking, nutrition and sleep that the formula does not model.
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