Enter one recent race. See what it predicts for every distance from the mile to the marathon, with the pace you need per kilometre and per mile.
mm:ss or h:mm:ss, e.g. 24:30 or 1:52:00. Use a race or time trial from the last 6 to 8 weeks.
| Distance | Predicted time | Pace /km | Pace /mi |
|---|
Predictions use the Riegel formula, T2 = T1 × (D2 / D1)1.06. They assume you are equally trained for the longer distance. From a 5K or 10K, the marathon number is your ceiling, not your likely result, unless your weekly volume already supports it. See 10K to marathon for the realistic range.
Enter one recent result and the calculator projects your time at every common distance, from the mile to the marathon. It uses the formula Pete Riegel published in 1977, which is still the standard for race equivalence: T2 = T1 × (D2 / D1)^1.06.
The exponent 1.06 captures how pace slows as distance grows. Double the distance and your time a little more than doubles, because you cannot hold the same pace twice as long.
Predictions are closest between neighbouring distances, 5K to 10K or 10K to half marathon, and when you have trained for the target distance. A 10K predicts a half marathon well if your long runs and weekly volume support 21 km.
Most runners who predict a marathon from a 5K or 10K miss the number. Short races are driven by speed and VO2max. The marathon is decided by your aerobic base, fuelling and how well you hold pace after 30 km. If your volume is low, treat the marathon prediction as a ceiling. The weekly mileage by goal guide shows the volume each target typically needs.
Within a few percent between neighbouring distances when you are trained for both. Accuracy drops as the gap grows, and the marathon is the least reliable prediction from a short race.
The Riegel formula: T2 = T1 x (D2 / D1)^1.06. It was published by Pete Riegel in 1977 and is the most widely used race equivalence model.
The formula assumes you are equally trained for every distance. A marathon also depends on your aerobic base, weekly volume and fuelling. With low volume, expect to run slower than the prediction.
Use your most recent all-out effort, ideally a race or solo time trial from the last six to eight weeks. A longer race usually gives a better marathon prediction than a mile.
Only if it was a genuine maximal effort over the full distance. Easy or tempo runs underestimate what you can do and make every prediction too slow.
Run Faster · Andreas Almgren · 10% off with RUNMASTERY
A prediction is a ceiling, the training decides whether you reach it. Andreas Almgren, the new New York Marathon champion, explains how he trains in Run Faster.
Get the ebook, 10% off →