Run one race. Predict every other.
Type a recent result. We use the Riegel formula to predict your finish time at every standard race distance — 5K to 50K.
From 10K in 50:00, here are your projected race times.
Find Marathon races →We use the Riegel formula: T₂ = T₁ × (D₂ / D₁)^1.06. Pete Riegel introduced it in 1981 after analyzing thousands of race results. The 1.06 exponent captures how runners slow down slightly when stepping up in distance.
Each row is the time we expect you to run at that distance, given the result you typed in. Tap any distance to find a race.
| Finish time | 5K | 10K | 15K | Half marathon | Marathon | 50K |
|---|---|---|---|---|---|---|
| 5K in 22:00 | 22:00 | 45:52 | 1:10:30 | 1:41:12 | 3:31:00 | 4:12:36 |
| 10K in 50:00 | 23:59 | 50:00 | 1:16:51 | 1:50:19 | 3:50:01 | 4:35:21 |
| Half in 1:45 | 22:50 | 47:35 | 1:13:08 | 1:45:00 | 3:38:55 | 4:22:04 |
| Marathon in 4:00 | 25:01 | 52:10 | 1:20:11 | 1:55:07 | 4:00:00 | 4:47:18 |
Riegel is most accurate when you predict from a similar distance — predicting marathon time from a 10K is reasonable; from a 1500m it is a stretch. Hilly courses, hot weather, fueling and pacing also matter. Treat predictions as a starting point, then refine with real race-day data.
The formulas and ranges above are grounded in the following peer-reviewed literature.
Origin of the Riegel formula T₂ = T₁ × (D₂/D₁)^1.06 used by this predictor. The 1.06 fatigue exponent is the most-cited running-prediction constant.
View bookUpdated empirical study (n>2,000 runners). Confirms Riegel's exponent fits well for distances within ~3× each other; predictions degrade beyond that range.
Read paperNow that you know your projected times, lock in a target race. SportPlan tracks running events worldwide.
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It uses the Riegel formula, an industry-standard equation that scales a known result up or down based on distance. Enter one recent race time and we project your time at every other standard distance.
Pete Riegel chose 1.06 after analyzing thousands of races. It reflects the small slowdown most runners experience as distance grows. Some athletes use 1.07 or 1.08 for more conservative ultra predictions.
You can, but with caution. Riegel is most reliable when the prediction distance is within ~3× of the known one. A 5K predicts a 10K well, an okay half, and a rough marathon. The closer the distances, the better the estimate.
No — Riegel assumes flat, dry conditions. Hilly courses, heat, wind and altitude can add 5-15% to your time. Use the prediction as a baseline and adjust based on the course profile.
The pace calculator converts between pace, time and distance for one race. The predictor uses one race result to estimate your time at every other distance — useful for picking a goal race or setting a marathon time from a recent half.