Running Pace Calculator
Work out your running pace, finish time or distance, and predict your times for the 5K, 10K, half marathon and marathon.
Pace = time ÷ distance; predictions by Riegel's formula · By Stuart Mathieson · Updated October 2026
Time
Pace
Results
Pace per km
Pace per mile
Time
Distance
Speed
Predicted race times
| Race | Time | Pace /km | Pace /mi |
|---|
Race predictions assume you ran your entered time at race effort and train for the longer distance. They are estimates, not guarantees.
How the pace calculator works
Pace is the time it takes to cover one kilometer or one mile. Choose what you want to calculate, and enter the other two:
Speed is the same thing the other way up - distance per hour - which is how treadmills show it. One mile is exactly 1.609344 km, so a pace per mile is 1.609344 times the pace per km.
Common paces
| Pace /km | Pace /mi | km/h | 5K | 10K | Half | Marathon |
|---|---|---|---|---|---|---|
| 4:00 | 6:26 | 15.0 | 20:00 | 40:00 | 1:24:23 | 2:48:47 |
| 5:00 | 8:03 | 12.0 | 25:00 | 50:00 | 1:45:29 | 3:30:59 |
| 6:00 | 9:39 | 10.0 | 30:00 | 1:00:00 | 2:06:35 | 4:13:10 |
| 7:00 | 11:16 | 8.6 | 35:00 | 1:10:00 | 2:27:41 | 4:55:22 |
Those finish times assume an even pace all the way. A half marathon is 21.0975 km (13.1 miles) and a marathon 42.195 km (26.2 miles).
Predicting race times
The calculator predicts your times at other distances with the formula published by Peter Riegel, an engineer and runner, in Runner's World in 1977 and in American Scientist in 1981:
T1 is your time over distance D1, and T2 the predicted time for distance D2. The exponent 1.06 is slightly above 1 because runners slow down as races get longer: doubling the distance takes a little more than double the time.
Worked example
A runner who finishes a 10K in 50:00 runs at 5:00 per km (8:03 per mile). The formula predicts a 5K in 23:59, a half marathon in 1:50:19 and a marathon in 3:50:01.
How reliable are the predictions?
- Riegel found this kind of relationship holds for efforts lasting roughly 3.5 to 230 minutes, so predictions from a 400 m sprint or to an ultramarathon are much rougher.
- The formula was fitted largely to elite performances. Many recreational runners slow down more over longer races, so marathon predictions from a 5K or 10K are often optimistic - training volume matters a lot for the marathon.
- Predictions from a race close to the target distance are more reliable: a half marathon predicts a marathon better than a 5K does.
- Heat, hills, wind and how you pace the race all change the result.
Frequently asked questions
How do I calculate my running pace?
Divide your time by the distance. A 10K in 50 minutes is 50 ÷ 10 = 5 minutes per km, or 8:03 per mile.
What pace do I need for a 4-hour marathon?
About 5:41 per km or 9:09 per mile, run evenly. Many runners aim a few seconds faster to allow for water stations and the crowd at the start.
How accurate is the Riegel race time predictor?
It is a reasonable guide between similar distances, such as 10K to half marathon. For the marathon it is often optimistic for recreational runners, who tend to slow down more than the formula assumes.
How do I convert pace per km to pace per mile?
Multiply by 1.609344. A pace of 5:00 per km (300 seconds) is 482.8 seconds per mile, or 8:03 per mile.
Sources
- Athletic Records and Human Endurance - Riegel PS, American Scientist 69(3):285-290, 1981
- Unit Conversion - National Institute of Standards and Technology (NIST)