Compute your pace in min/km and predict your time at 5K, 10K, half marathon or marathon from a recent race, using the Riegel formula.
Prediction (Riegel formula)
- 1 km4:214:21/km
- 5 km23:594:48/km
- 10 km50:005:00/kmcurrent
- Half marathon1:50:195:14/km
- Marathon3:50:015:27/km
The Riegel formula assumes adequate training for the target distance. For marathons it tends to overestimate.
Pace is the time it takes you to run one kilometre, expressed in min/km. Knowing your paces lets you train in the right zones and predict your time on target races.
The Riegel formula
Riegel (1981) predicts your time at a target distance from a known one: T2 = T1 · (D2/D1)^1.06. It works well between 5 minutes and 3-4 hours of duration. For the marathon it tends to overestimate (reality will be 2-5% slower) because it assumes adequate training for that distance.
How to use it for training
If your goal is to drop your 10K time, first run a 5K all-out. Use Riegel to predict your 'natural' 10K. The gap between that and your goal is what you need to close with more volume and specific intervals at 10K pace.
Frequently asked questions
How accurate is Riegel?+
Good between 5 minutes and 3-4 hours of total duration. For marathons it usually overestimates (real time will be 2-5% slower). For very short distances (<3 min) it underestimates.
Why is my real pace worse than predicted?+
Riegel assumes adequate training for the target distance. If you're doubling distance (5K → 10K), you need weeks of mileage to actually achieve it.