Running 10 km in 50 minutes is a pace of 5:00 per kilometre, or 8:03 per mile, at a speed of 12 km/h. At the same effort the Riegel formula predicts about a 1:50 half marathon and a 3:50 marathon, though marathon predictions assume matching training.
How do you calculate running pace?
Pace is time divided by distance. A 10 km run in 50 minutes is 50 ÷ 10 = 5 minutes per kilometre. To convert to miles multiply by 1.609: 5:00/km is 8:03 per mile. Speed is the reverse, distance divided by time: 10 km in 50 minutes is 12 km/h. The calculator does the conversion, gives your total time and lists what the same pace would mean over standard race distances.
Predicting race times with the Riegel formula
The Riegel formula (T₂ = T₁ × (D₂ ÷ D₁)1.06) estimates your time over another distance from one performance. The exponent 1.06 captures how pace slows as the distance grows. From a 50-minute 10K the formula gives about 1:50 for a half marathon and 3:50 for a marathon. These work best if you have trained for the longer distance. A runner who only does 10K training will often slow much more than predicted in a marathon.
Common pace benchmarks
| Pace per km | 5K | 10K | Half marathon | Marathon |
|---|---|---|---|---|
| 4:30 | 22:30 | 45:00 | 1:35 | 3:09 |
| 5:00 | 25:00 | 50:00 | 1:45 | 3:30 |
| 5:30 | 27:30 | 55:00 | 1:56 | 3:52 |
| 6:00 | 30:00 | 1:00:00 | 2:06 | 4:13 |
| 7:00 | 35:00 | 1:10:00 | 2:27 | 4:55 |
These are straight-line times at a constant pace. Most runners slow a little in the second half, and real marathon times are usually 5% to 10% slower than a flat extrapolation from a 10K.
Using pace in training
- Easy runs should feel conversational, often 60 to 90 seconds per km slower than 10K pace.
- Tempo runs sit near your 10K to half marathon pace.
- Intervals use 5K pace or faster over shorter reps.
In Dutch this tool is called a hardloop calculator. Plan your fuel with the Calorie Calculator and the Protein Calculator for recovery.
How to use this calculator
- Enter the distance of your run and pick kilometres or miles.
- Add your finish time in hours, minutes and seconds.
- Read your pace per km and per mile and your speed.
- Check the race table to see predicted times for longer distances.
Key figures at a glance
| Pace | time ÷ distance |
|---|---|
| Mile | 1.609 km |
| Riegel exponent | 1.06 |
| Half marathon | 21.0975 km |
| Marathon | 42.195 km |
Frequently asked questions
Divide your total time by the distance in km. For 10 km in 55 minutes that is 5:30 per km.
For recreational runners, 50 to 60 minutes is common. Under 45 minutes is a strong club-level time.
Multiply by 1.609. For example 5:00/km is 8:03/mile.
It is optimistic if your longest runs are short. Add 5% to 10% if you have not trained long distances.
T₂ = T₁ × (D₂ ÷ D₁)^1.06, an empirical formula for predicting race times from a previous result.