Running pace / race predictor
Convert one recent race or time trial into a realistic pace target for another distance.
Predict race time and pace
Best when the known result is recent, hard, and reasonably close to the target distance.
Close-enough distance jump. Conditions and pacing still matter.
The useful number, with the asterisks left in
What this number means
Race predictors estimate what one performance might imply for another distance if your endurance, pacing, terrain, and conditions are reasonably matched.
This calculator uses the Riegel formula, a simple endurance-performance model commonly written as T2 = T1 x (D2 / D1)^1.06.
What it does not know
A 5K does not automatically predict a marathon if you have not trained for marathon-specific fatigue, fueling, and durability.
Weather, hills, surface, shoes, race tactics, course accuracy, and how recent the performance was can all matter more than the formula.
How to use it
Use a recent hard race or honest time trial. The closer the known distance is to the target distance, the more useful the prediction tends to be.
For training, start slightly slower than the prediction if you are unsure. A controlled first half beats calculator confidence followed by a late collapse.
When not to trust it
Be careful when jumping from short races to long races, from flat roads to trails, or from cool-weather performances to hot-weather goals.
Do not use an old personal best as if it describes current fitness.
Caveats
- Large distance jumps are automatically flagged.
- The formula assumes similar fitness expression across distances.
- Course and conditions can swamp small differences in predicted pace.
Examples
- A 25:00 5K predicts roughly 52:10 for 10K by Riegel.
- A 1:50:00 half marathon predicts roughly 3:49:00 for the marathon, before course and fueling caveats.
Where the method comes from
- Riegel P. Athletic Records and Human Endurance. American Scientist. 1981.
- U.S. Department of Health and Human Services. Physical Activity Guidelines for Americans, 2nd edition.
- CDC. How to Measure Physical Activity Intensity.