Estimate a time at a new distance from a known race using Riegel's formula: T2 = T1 × (D2 / D1)^1.06.
| Predicted (min) | – |
Use this calculator to guess a finish time at a second distance from a race you have already run. Enter the known distance, the time for that distance, and the target distance. Distances can be in kilometres (km) or miles (mi); the unit selector converts both distances automatically before the calculation.
Predicted time = known time × (target distance ÷ known distance)^1.06. Time is decimal minutes: 20 is 20:00, 41.5 is 41:30. A 20-minute 5 km often predicts a bit over 41 minutes for 10 km. The 1.06 exponent is a fatigue fudge, not a physiology lab.
The estimate works best when both races are recent and similar (road, not trail or track with different tactics). It does not account for weather, hills, or a bad taper.
Known distance: Distance you already ran. Enter km or mi.
Time: Time for that distance, in decimal minutes.
Target distance: Distance you want a guess for. Use the same unit family as the known distance.
Predicted: Estimated time in decimal minutes.
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