Running pace per km / mile and finish-time predictor for common race distances.
Updated
Predicted finish times if you ran each distance at your current endurance level. Based on T₂ = T₁ · (D₂/D₁)^1.06.
| Distance | Predicted finish time | Pace |
|---|---|---|
| 1 mile(1.61 km / 1.00 mi) | 7:13 | 4:29 /km |
| 5K(5.00 km / 3.11 mi) | 23:59 | 4:48 /km |
| 10K(10.00 km / 6.21 mi) | 50:00 | 5:00 /km |
| Half marathon(21.10 km / 13.11 mi) | 1:50:19 | 5:14 /km |
| Marathon(42.20 km / 26.22 mi) | 3:50:01 | 5:27 /km |
Quick start
Enter a distance and a time. The calculator returns pace per km / mile, average speed, and predicted finish times for the standard race distances using Riegel's formula.
Switch between kilometers and miles for the distance input.
Type the distance you ran and the time as M:SS or H:MM:SS (e.g. 25:30 or 4:15:00).
Pace per km and per mile, speed in km/h and mph, and a Riegel-predicted finish time for 1 mile, 5K, 10K, half-marathon and marathon.
In-depth guide
Enter a distance and a time and the calculator returns pace per km and per mile, average speed in km/h and mph, and predicted finish times for the standard race distances using Riegel's 1981 endurance formula. Useful for race planning, workout pacing and comparing efforts across distances.
Two ways to express the same number:
Conversion: pace (min/km) = 60 / speed (km/h). A 12 km/h pace is 5:00/km; a 10 mph pace is 6:00/mi.
Pete Riegel's 1981 paper proposed an endurance scaling law that has held up across forty years of race data:
T₂ = T₁ · (D₂ / D₁)^1.06
The 1.06 exponent encodes the rule that pace slows about 6% per doubling of distance for trained runners. A 5K time of 22:00 implies ~45:30 for 10K (a 6% slow from the 5K pace), ~1:40:30 for the half-marathon, and ~3:31 for the marathon.
Riegel's formula assumes endurance is the limiting factor, which is true for distances roughly between 1 mile and the marathon for trained runners. Outside that range:
Three places this calculator earns its keep:
No. The pace and finish-time predictions run entirely in your browser as you type. Nothing is sent to a server, stored, or logged.
Riegel's formula (1981): T₂ = T₁ × (D₂/D₁)^1.06. The 1.06 exponent encodes the empirical observation that pace slows by about 6% per doubling of distance for trained runners. It's the most-cited endurance prediction model and works well from 1 mile up to the marathon.
Within roughly 2–5% for trained runners predicting from a half-distance event upward. It overestimates marathon performance for runners whose endurance training is light (the 6%/doubling slope is steeper at high distances when fueling, heat and pacing dominate). It underestimates short-distance speed for highly anaerobic athletes.
Riegel's model breaks down at ultra distances (50K+) because the dominant factors shift from cardiovascular endurance to fueling, heat regulation and pacing. We cap predictions at the marathon to avoid implying a precision the formula doesn't have.
Highly individual. As rough public-data brackets: under 30 min is a typical recreational target, 22–25 min for regular runners, 18–20 min for serious amateurs, sub-15 for elite. Age and sex matter — your own trend over weeks matters more than any benchmark.
Riegel's exponent (1.06) was fit on running data. Cycling has a much flatter pace-vs-distance curve (drafting, gearing, terrain dominate); swimming sits between. For running this tool is reliable; for other sports treat the predictions as illustrative only.
Use M:SS or H:MM:SS format — '25:30' for a 25-and-a-half-minute 5K, or '4:15:00' for a 4-hour-15-minute marathon. Distance is in kilometers; switch the pace output row to read in mi/km depending on which side of the Atlantic you train.
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