Running Pace Calculator
It converts a distance and finishing time into pace per kilometer and per mile, speed in km/h and mph, and predicted times at every standard race distance.
Pace
8:00 / mi
Per mile
8:00
Per kilometer
4:58
Speed mph
7.50
Speed km/h
12.07
Per 400 m
1:59
Total time
40:00
| Race | Predicted time | Pace / mi |
|---|---|---|
| 5K | 24:09 | 7:46 |
| 10K | 50:22 | 8:06 |
| Half marathon | 1:51:07 | 8:29 |
| Marathon | 3:51:41 | 8:50 |
What it calculates
It converts a distance and finishing time into pace per kilometer and per mile, speed in km/h and mph, and predicted times at every standard race distance.
Why it matters
Training plans are written in pace, races are run to a target time, and converting between them in your head mid-run is not realistic.
Who it's for
Runners planning race pace, coaches setting training zones, and anyone working toward a 5K, half or marathon goal.
Formula
- d
- Distance covered
- t
- Total time
- 1.06
- Riegel's fatigue exponent for race prediction
Worked example
10 km in 50 minutes
- 1Pace = 3,000 s ÷ 10 km = 300 s/km
- 2300 s = 5:00 per kilometer
- 3Speed = 10 ÷ (3000 ÷ 3600) = 12 km/h
5:00 per km, 8:03 per mile, 12 km/h — predicting a 3:50 marathon
How the running pace calculator works
Pace is time divided by distance, and speed is its reciprocal. Race predictions use Riegel's formula, T₂ = T₁ × (D₂/D₁)^1.06, where the exponent above 1 captures the fact that pace slows as distance grows. It is accurate within a few percent for distances within roughly a factor of four, and it assumes you have trained appropriately for the longer distance.
Pace is time divided by distance; speed is its reciprocal. The two get confused constantly — 5:00 per kilometer and 12 km/h describe the same run.
Race predictions use Riegel's formula, where the exponent above 1 captures the fact that pace slows as distance grows. It is accurate within a few percent for distances within roughly a factor of four, and it assumes you have actually trained for the longer race.
Common mistakes
- Starting a race at a pace pulled from a short training run, then fading badly.
- Treating a marathon prediction from a 5K time as achievable without marathon-specific training.
- Confusing pace, which is minutes per distance, with speed, which is distance per hour.
Tips and best practice
- Riegel predictions assume adequate endurance training; without long runs, the marathon estimate will be optimiztic.
- Most easy training should be run considerably slower than race pace.
Frequently asked questions
How do I calculate running pace?
Divide total time by distance. Ten kilometers in 50 minutes is 5:00 per kilometer, or about 8:03 per mile.
How accurate are race time predictions?
Riegel's formula is usually within a few percent for distances within a factor of about four, provided you have trained specifically for the longer race.
What is a good 5K time?
It varies enormously by age and experience. Roughly, 30 minutes is a solid recreational time, 25 minutes is a well-trained club runner, and under 20 is competitive.
What is the difference between pace and speed?
Pace is time per unit distance (5:00 per km) and speed is distance per unit time (12 km/h). They are reciprocals of each other.
How do I convert pace per km to pace per mile?
Multiply by 1.609. A 5:00 per kilometer pace is about 8:03 per mile.
Related calculators
Methodology & trust
- Formula source
- Pete Riegel's endurance prediction model (1977), exponent 1.06.
- Last updated
- 2026-07-28
- Privacy
- Every calculation runs in your browser. No inputs are sent to a server or stored.
- Accessibility
- Keyboard navigable, labeled inputs and WCAG AA color contrast.