10K Time From 5K — Riegel Predictor
If you have a 5K in the bank, the 10K is the easiest prediction in distance running to make — the two races sit close enough together that the math barely has to stretch. Enter your 5K time:
Predicted time
52:07
Predicted pace of 5:13/km.
How we got this number
T₂ = T₁ × (D₂ ÷ D₁)^1.06 = 25:00 × (10 ÷ 5)^1.06 = 52:07
| Distance | Predicted time | Predicted pace |
|---|
Worked example: 25:00 for 5K
T₂ = 25:00 × (10 ÷ 5)^1.06 = 52:07, a pace of 5:13/km (8:23/mile).
Three reference points, so you can place yourself without doing the arithmetic:
| 5K result | Predicted 10K | Predicted 10K pace |
|---|---|---|
| 22:00 | 45:52 | 4:35/km |
| 25:00 | 52:07 | 5:13/km |
| 30:00 | 1:02:33 | 6:15/km |
Notice the pattern: whatever your 5K, the predicted 10K is your 5K time multiplied by 2.085. The slowdown is proportional, so the faster you are, the fewer absolute seconds per kilometer you give away.
Why this is the jump the formula gets right
Riegel’s equation was fitted to record performances, which is exactly why it tends to run fast for ordinary runners over long distances. The 5K-to-10K step dodges that problem, because the two races draw on nearly the same physiology and the same training. When Vickers and Vertosick tested the formula against 2,303 recreational runners in 2016, they found no evidence that the 10K predictions were miscalibrated — the coefficient came out statistically indistinguishable from a perfect one, at p = 0.9. The half marathon held up too. The marathon did not.
So this page is where the predictor is at its strongest. If you are moving up in distance, taking one step at a time and re-predicting from your newest result is a far better habit than jumping straight to the marathon from a short race.
Turning the prediction into a race plan
The predicted time is your ceiling on a good day, not a schedule. Two things move it: the second half of a 10K asks for aerobic endurance a 5K never tests, and the pacing error that costs you ten seconds in a 5K costs you a minute over twice the distance. Go out at the predicted pace, not under it.
Ready for the next step up? The half marathon prediction from your 10K is the natural follow-on, and the race time predictor handles any pair of distances you want to feed it.
Frequently asked questions
What 10K time does a 25-minute 5K predict?
About 52:07, which is 5:13/km or 8:23/mile. The 5K itself was run at 5:00/km, so the predicted 10K pace is thirteen seconds per kilometer slower — that slowdown is built into the formula, not a penalty for you.
Why is the predicted 10K pace slower than my 5K pace?
Because the exponent in Riegel's equation is 1.06 rather than 1. Sustainable pace falls as the effort lengthens, so doubling the distance multiplies the time by 2.085 instead of 2.
How reliable is a 10K predicted from a 5K?
This is the most reliable jump on the whole chart. When 2,303 recreational runners were checked against the formula, the 10K predictions showed no evidence of miscalibration at all.
Can I predict a marathon straight from my 5K?
The math will produce a number, but it is the worst use of the formula. A 25-minute 5K yields a 3:59:47 marathon, and for most recreational runners that is far too fast. Predict the next distance up, then re-predict from that.
Does my 5K need to be a race, or is a time trial fine?
A hard, honest time trial works. What matters is that the effort was maximal for the whole 5K — a tempo run you could have pushed harder on will feed an optimistic 10K prediction.
Sources
Written by Lucas Silva · Reviewed by Lucas Silva · Updated on August 15, 2026