How to use the race pace calculator
- Choose whether to find your pace (from a time) or your finish time (from a pace).
- Pick a race distance or enter a custom distance in km or miles.
- Enter the race time, or the pace per mile or per km.
- See your pace, speed and the equivalent times at other distances.
How the calculation works
Pace is time divided by distance; speed is distance divided by time. The calculator converts between miles and kilometers using 1 mile = 1.609344 km. Official race distances are used for presets: the marathon is 42.195 km and the half marathon 21.0975 km.
The predictions table uses Peter Riegel’s endurance formula, which estimates how race times scale with distance. It is most useful between about 1.5 km and the marathon, for runners who have trained for the target distance.
Formula
Worked examples
10K in 52:30
3,150 s ÷ 10 km = 315 s/km = 5:15 per km. Per mile: 315 × 1.609344 = 506.9 s = 8:27 per mile. Speed = 11.43 km/h (7.10 mph).
Marathon at 8:30 per mile
42.195 km = 26.219 mi. 26.219 × 510 s = 13,371.6 s = 3:42:52.
Assumptions and limitations
- Predictions assume equivalent training and similar conditions. Heat, hills, wind, altitude and pacing strategy all change real results.
- Riegel’s formula tends to be optimistic for long races if training volume is low.
Frequently asked questions
What is a good 5K pace?
It varies widely by age, experience and fitness. Many recreational runners finish 5K at 8-12 minutes per mile; use the calculator to set a realistic target from a recent race.
How do I convert pace per km to pace per mile?
Multiply the pace in seconds per km by 1.609344. 5:00 per km becomes 8:03 per mile.
What pace do I need for a 4-hour marathon?
About 9:09 per mile, or 5:41 per km, held for the full 42.195 km.
Sources and references
- Riegel PS. Athletic records and human endurance. American Scientist. 1981;69(3):285-290.