Pace and speed
Runners usually talk in pace: minutes per mile or per kilometer. Pace is time divided by distance; speed is the inverse. A 25-minute 5K (3.1 miles) is a pace of 5:00 per km or 8:03 per mile, a speed of 12 km/h (7.5 mph).
Predicting race times
Peter Riegel, an engineer and marathoner, showed in 1981 that race times across distances follow a simple rule: T₂ = T₁ × (D₂ ÷ D₁)^1.06. Running a 25-minute 5K predicts about 52:07 for 10K, 1:55:00 for a half marathon and 3:59:47 for a marathon.
These predictions assume you have trained for the longer distance. For the marathon in particular, many runners are slower than predicted unless they have done the long runs.
Common pace targets
| Goal | Pace per mile | Pace per km |
|---|---|---|
| 30-minute 5K | 9:39 | 6:00 |
| 1-hour 10K | 9:39 | 6:00 |
| 2-hour half | 9:09 | 5:41 |
| 4-hour marathon | 9:09 | 5:41 |
Enter times as hours:minutes:seconds (1:20:30) or minutes:seconds (25:00).
How this works
The page converts the distance to kilometers (1 mile = 1.609344 km), reads the time in seconds, and divides time by distance for the pace per kilometer, then multiplies by 1.609344 for the pace per mile. Speed is distance divided by time in hours. Race predictions apply Riegel's formula with the exponent 1.06. Everything runs in your browser.
Frequently asked
How do I calculate running pace?
Divide your time by the distance. 25 minutes for 5 km is 5:00 per km.
What is a good 5K pace?
Recreational runners often run 8–11 minutes per mile; a sub-25 5K is about 8:03 per mile.
How accurate are race predictions?
Good for distances you have trained for; marathon predictions from short races are often optimistic.
How do I enter the time?
Use h:mm:ss or mm:ss, for example 1:45:00 or 25:30.
Sources
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/health/pace-calculator/