Running Race Time Predictor (Riegel Formula)
Predict a race time from a recent result.
Enter your values
Enter the finishing time in total minutes.
ⓘ Live results
Results
- Predicted time
- 1h 39m 18s
- Predicted pace
- 4.71 min/km
- Total minutes
- 99.3
Quick answer
The Riegel formula scales a known race time to a new distance using a fatigue exponent of about 1.06.
T2 = T1 x (D2/D1)^1.06
How to use the Running Race Time Predictor (Riegel Formula)
- 1Enter a recent race distance and finishing time in minutes.
- 2Enter the target distance you want to predict.
- 3The Riegel formula works best between similar distances (e.g. 10K to half marathon), not extreme jumps.
Inputs explained
- Known time(min)
- Enter the finishing time in total minutes.
Worked example
Using the values the calculator loads with:
Inputs
- Known distance10 km
- Known time45 min
- Target distance21.1 km
Results
- Predicted time1h 39m 18s
- Predicted pace4.71 min/km
- Total minutes99.3
Frequently asked questions
Why not linear scaling?
Fatigue means pace naturally slows over longer distances, which the 1.06 exponent captures.
How accurate is this?
It's a solid estimate for trained runners but can overstate endurance for undertrained long-distance efforts.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.