Running Pace Calculator
Run a 5K, we'll predict your half-marathon. Riegel's endurance-decay formula gives you a realistic target across every distance.
Inputs
Result
- Pace5m 00s/km
- Predicted 5K25m 00s
- Predicted 10K52m 07s
- Predicted Half1h 55m 00s
- Predicted Marathon3h 59m 47s
Calculations run locally in your browser. Nothing is sent to a server.
Riegel (1981): T2 = T1 × (D2 / D1)^1.06. The 1.06 exponent reflects endurance decay over distance. Best fit for runners < 70% VO₂max at race pace.
References
Why is Riegel slightly optimistic for marathon?
Riegel under-predicts by ~3–5% for distances above your training peak. Plug in 10K or half data for the most accurate marathon prediction.
Does this account for hills, heat, wind?
No. Flat-course, temperate conditions. Add 2-5% per category for tough courses.
Is this what Ascend uses?
Yes, for goal forecasting + race-day pacing on Club tier.
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