Running pace calculator: time, pace and speed
This pace calculator turns a distance and a time into a pace (min/km or min/mile) and a speed (km/h or mph). It also predicts your time over another distance with the Riegel formula: T2 = T1 x (D2 / D1)^1.06. In a few seconds you know how fast you ran and what that means for your next race.
Fill in the fields to see the result.
How to use it
- Choose your unit: kilometers or miles.
- Enter the distance you ran and your time (for example 10 and 50:00, or 1:45:00).
- Read your average pace and speed.
- Choose another distance to see the time predicted by the Riegel formula.
The method
Pace is time divided by distance: 50 minutes for 10 km is 5 minutes per kilometer. Speed is the opposite: distance divided by time, brought back to one hour. No estimate here, just exact math.
The prediction uses the formula of Peter Riegel, an American engineer who published it in 1981 in American Scientist. By comparing world records over different distances, he saw that time doesn't increase in proportion to distance: it increases a bit faster, with an exponent of 1.06. So doubling the distance means a bit more than doubling the time, because you can't hold the same pace for longer. It's simple, and it works well as long as the two distances stay close.
An example
You run 10 km in 50:00. Your pace is 5:00 per km (8:03 per mile) and your speed is 12 km/h. With Riegel, that 10K gives 23:59 for 5K, 1:50:19 for a half marathon and 3:50:01 for a marathon.
Limitations
The Riegel formula was built on world records, so on runners highly trained for each distance. It doesn't know whether you've done the long runs you need, whether it'll be hot, or whether there's elevation. A study of 2,303 recreational runners (Vickers and Vertosick, 2016) shows that it's reliable up to the half marathon but clearly underestimates marathon time: for half the runners, it predicted a time at least 10 minutes too fast. The bigger the gap between the two distances, the shakier the prediction. It doesn't apply to trail running: elevation changes everything.
Frequently asked questions
How do you calculate your pace per km?
Divide your time by the distance. 50 minutes for 10 km is 5 minutes per km. The calculator does it for you, in km or in miles.
How do you convert a speed in km/h into a pace?
Divide 60 by your speed in km/h to get minutes per km. At 12 km/h, you run 5:00 per km; at 10 km/h, 6:00 per km.
Is the Riegel formula reliable for the marathon?
Less so than for shorter distances. For recreational runners, it often predicts a marathon that is too fast (Vickers and Vertosick, 2016). Keep a margin, especially if you do few long runs.
Which distance should you use to predict your time?
The one closest to your target race, and a recent race you ran all out. A recent half predicts a marathon better than a 5K does.
Sources
- Riegel, P. S. (1981). Athletic Records and Human Endurance. American Scientist, 69(3), 285-290.
- Vickers, A. J. and Vertosick, E. A. (2016). An empirical study of race times in recreational endurance runners. BMC Sports Science, Medicine and Rehabilitation, 8, 26.
What if ELYO worked it out for you?
ELYO reads the workouts from your watch and works out your paces from your real runs, not from a single race. It then adjusts your plan to what you can really hold in training.