Race Time Calculator: Predict Any Race From One Result
One honest race result is enough to sketch a target for a longer — or shorter — distance. The Riegel formula does the scaling.
What is the Race Time Calculator?
The Riegel formula predicts a new race time by scaling a known time with the ratio of the two distances raised to the power 1.06, which reflects that pace fades slightly as distance grows. Enter a recent race you actually ran, plus the distance you want to predict. It is a performance estimate, not a guarantee — training, course, and weather all shift real results.
How to use it
- Enter your known race time in minutes and its distance in kilometres.
- Enter the target race distance in kilometres.
- Read your predicted time in minutes and hours:minutes.
Worked example
A 25-minute 5 km predicts a 10 km time of 52.12 minutes (25 × 2^1.06), shown as 0:52.
How do I predict my 10 km time from a 5 km race?
Scale your 5 km time by the distance ratio raised to 1.06: a 25-minute 5 km predicts about 52.12 minutes for 10 km, because doubling the distance costs slightly more than double the time. The 1.06 exponent captures that fade; without it you would wrongly predict exactly 50 minutes. Use the result as a training target, then adjust after a real race at the new distance.
Frequently asked questions
How accurate is the Riegel prediction?
It is usually close for nearby distances, but predictions far from your known race — say from 5 km to a marathon — carry much more uncertainty.
Should I use my best or a recent time?
Use a recent race run in similar conditions; an old personal best on a fast course will flatter the prediction.