Conditioning · Riegel
Pace & Race Predictor
Turn one finish time into your pace, speed, and equivalent times at every standard distance — with Riegel’s published limits marked.
Negative or non-numeric entries are ignored rather than subtracted.
Pace · per mile
8:03/mi
That's 25:00 for 5K. Pace and speed are exact arithmetic — it's the predicted times below that carry assumptions.
Splits & speed
Equivalent race times
| Distance | Predicted | Pace / mi |
|---|---|---|
| 1 mile | 7:31 | 7:31 |
| 5K | 25:00 | 8:03 |
| 10K | 52:07 | 8:23 |
| Half marathon | 1:55:00 | 8:46 |
| Marathon * | 3:59:47 | 9:09 |
* Outside the range Riegel published this formula for — either the predicted time falls beyond his 3.5-to-230-minute window, or the jump in distance is more than fivefold. Treat a starred row as a rough ceiling, not a target.
Riegel's model, T₂ = T₁ · (D₂/D₁)^1.06, from “Athletic Records and Human Endurance” (American Scientist, 1981). It assumes you have trained specifically for the target distance and that the course and conditions are comparable — not simply that your fitness is even. In the largest published test of it, the marathon prediction came out at least 10 minutes too fast for half of 2,303 recreational runners.
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How this is calculated
Pace is your finish time divided by the distance — exact arithmetic, with kilometres and miles converted at the exact factor 1 mile = 1.609344 km. The equivalent race times use Riegel's formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06, where T₁ and D₁ are the race you actually ran.
- 01Take your finish time in seconds and divide by the race distance to get pace per kilometre; multiply by 1.609344 for pace per mile.
- 02Speed is the same figure inverted: distance divided by elapsed hours.
- 03For each standard distance, scale your time by the distance ratio raised to the power 1.06 — the exponent Riegel fitted to world-record performances.
- 04Flag any predicted row that falls outside the 3.5-to-230-minute window Riegel fitted, or that represents more than a fivefold jump in distance, because those are extrapolations rather than predictions.
EstimatePace and speed are exact. The equivalent race times are estimates, and the marathon row is the least reliable number on this page — it is the one the published validation study found most over-optimistic.
What this assumes
- · The official distances are the World Athletics standards: Road Mile 1609.344 m, 5 km, 10 km, half marathon 21.0975 km, marathon 42.195 km.
- · Riegel fitted the 1.06 exponent to world records for efforts lasting roughly 3.5 to 230 minutes. He called that the "endurance range"; outside it the time-versus-distance relationship stops being a straight line, so we mark those rows rather than hide them.
- · Those records were set by specialists at each distance, so the formula assumes you have trained for the distance you are predicting. It cannot know your weekly mileage — and mileage is what decides whether you hit a long-distance number.
- · Comparable course and conditions. Hills, heat, wind and altitude are not in the model.
- · Vickers & Vertosick (2016) tested the formula on 2,303 recreational runners: well calibrated up to the half marathon, but marathon times at least 10 minutes too fast for half of them, with weekly training mileage a stronger predictor than any short-race time. Race a marathon at the pace shown here off a 5K and the likely outcome is running out of fuel in the last 10 km.
Sources
- [1]NIST Guide to the SI, Appendix B.9 — Conversion Factors — 1 mile = 1.609344 km, an exact conversion
- [2]World Athletics Book of Rules — Technical Rules C2.1, Part VII (Road Races) — the official distances: Road Mile 1609.344 m, 5 km, 10 km, Marathon 42.195 km
- [3]World Athletics — Half Marathon discipline — the half marathon at 21.0975 km
- [4]Riegel, P.S. (1981). Athletic Records and Human Endurance. American Scientist 69(3):285–290 — the prediction formula, and the 3.5–230 minute "endurance range" it was fitted over
- [5]Vickers, A.J. & Vertosick, E.A. (2016). An empirical study of race times in recreational endurance runners. BMC Sports Sci Med Rehabil 8:26 — 2,303 runners: Riegel was well calibrated to the half, but gave marathon times at least 10 minutes too fast for half of them
Last reviewed October 2026
Use the marathon row as a ceiling, not a plan
If you pace a real marathon off a predicted time that came from a 5K or a mile, the most likely outcome is a positive split: you run out of fuel in the last 10 km and finish slower than if you had started 15 to 20 seconds per mile easier. Build the distance gradually and let a long run, not a calculator, set your race pace.
Exercise Legend is not a medical authority and this tool does not provide medical advice. Talk to a doctor before starting marathon training if you have a cardiovascular or metabolic condition, or if you get symptoms during exercise.