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Calculate race pace per mile or kilometer, finish time, and split times for any distance. Plan pacing for 5K, 10K, half marathon, and marathon.
Estimate VO2 max from race times, Cooper 12-minute test, or resting heart rate. Measure aerobic fitness for running and cycling training.
Calculate heart rate training zones from max HR, lactate threshold, or Karvonen formula. Set easy, tempo, threshold, and interval zones for running.
Predicted time at distance D2 from known time T1 at distance D1. Exponent 1.06 works for most trained runners; 1.08–1.10 for less endurance-trained athletes.
T2 = T1 × (D2 / D1)^1.06Use the same units for both distances — kilometers or miles. Marathon = 42.195 km or 26.219 miles; half marathon = 21.0975 km or 13.109 miles.
T_marathon = T_half × (42.195 / 21.0975)^1.06 ≈ T_half × 2.085Riegel assumes adequate preparation for the target distance. A fast 10K runner without marathon mileage may predict 5–15% faster than achievable. Add endurance training weeks before trusting long-distance predictions.
Adjusted prediction = Riegel × Training factor (0.95–1.05)Updated: July 2026
1:45 half = 105 min. Predicted marathon: 105 × (42.195/21.0975)^1.06 ≈ 219 min = 3:39:00. Requires 16+ weeks marathon-specific training.
44 min 10K predicts marathon ~3:42. Less reliable than half marathon input — add 3–5% buffer unless weekly mileage exceeds 50 miles.
20 min 5K Riegel prediction ~3:28 marathon. Short-distance predictions overestimate marathon ability without long-run base — treat as ceiling, not plan.
Riegel extrapolates endurance from speed. A fast 5K predicts an optimistic marathon if weekly long runs are under 16 miles. Use half marathon results or add 5–10% to short-distance predictions.
Fitness changes significantly over months. Use a performance from the last 8–12 weeks. Older results may over- or under-predict depending on training trajectory.
The Riegel formula predicts race times at one distance from a performance at another, assuming equivalent effort. It helps set realistic marathon goals from recent 5K, 10K, or half marathon results. Predictions assume proper marathon-specific training and pacing.