Formula
Pete Riegel's endurance formula raises the distance ratio to 1.06:
Target minutes = known minutes × (target km / known km)^1.06
The exponent is slightly above 1, so doubling the distance takes a little more than twice the time. A marathon has its own pace page once you already have a finish time.
Assumptions
- Both distances are in kilometers.
- The known effort is similar to the target effort.
- The formula is a curve fit, not a promise.
Worked example
A 5 km in 25 minutes predicts 52.12 minutes for 10 km.
Input definitions
- Known time
- A finish time you have already run, in minutes.
- Target distance
- The race you want to estimate.
Limitations
Course, weather, and training are outside the exponent. Do not treat the prediction as a required pace.
Questions
Why not double the time for double the distance?
Riegel's 1.06 exponent adds a small endurance penalty as the distance grows.
Can I enter a marathon?
Yes, as 42.195 km. The marathon pace page is for when you already know the finish time.