Three calculations
Pick what you want to find with the tabs at the top. Distance, time and pace are linked: if you know two of them, the calculator gives you the third.
- Pace — Enter a distance and a time to see your pace per km and per mile, plus your speed (km/h, mph). Handy for looking back at a race or a training run.
- Finish time — Enter a distance and a target pace to get your finish time. Use it to check your finish time at a given pace.
- Distance — Enter how long you ran and at what pace to get the distance. Useful when you timed a run without GPS.
Set the distance with the 5K, 10K, Half and Marathon buttons or type your own, and choose kilometers or miles. The pace field follows the unit you pick.
Pace vs. speed
Pace answers “how many minutes per kilometer?”, speed answers “how many kilometers per hour?”. They express the same relationship in opposite ways, so one gives you the other.
- A pace of 5:00/km = 12 km/h (7.46 mph)
- A pace of 6:00/km = 10 km/h
Runners mostly talk in pace, while treadmills usually show speed. Just remember: a lower pace is faster, a higher speed is faster.
The formulas
- Pace = time ÷ distance
- Time = distance × pace
- Distance = time ÷ pace
- Speed (km/h) = distance (km) ÷ time (hours)
- Pace per mile = pace per km × 1.609344
For example, 10 km in 50:00 is a pace of 5:00/km, or 8:03 per mile. A marathon (42.195 km) at 5:00/km takes 42.195 × 5 min = 210.975 min, which is 3:30:59. Results are rounded to the nearest second.
Using split times to plan your race pace
Below the result, the split table shows your elapsed time at every kilometer (or mile), with the half-marathon point (21.0975 km) and the finish marked. Set a goal time and use it to check your watch during the race.
If you want to run a marathon under 4 hours, use the Pace tab rather than Finish time: enter 42.195 km and 4:00:00. You need about 5:41/km (9:09 per mile), and the split table shows 56:53 at 10 km, 2:00:00 at halfway and 2:50:38 at 30 km. The table assumes an even pace from start to finish, so it is wise to leave a few tens of seconds of margin for hills, aid stations and fatigue late in the race.
Race predictions and their limits
The result also shows predicted times for 5K, 10K, half marathon and marathon, based on your current result. It uses the formula Pete Riegel published in American Scientist in 1981:
T2 = T1 × (D2 ÷ D1)^1.06
T1 is the time you know, D1 its distance and D2 the distance you want to predict. The exponent 1.06 means that doubling the distance takes a bit more than twice as long (about 2.085 times). For example, a 45:00 10K predicts about 1:39:17 for the half marathon and about 3:27:01 for the marathon.
These are estimates only.
- Riegel looked at efforts lasting about 3.5 to 230 minutes. A 60:00 10K predicts a marathon of about 4:36:01, which is over 230 minutes, so the table marks it as outside the range.
- The exponent 1.06 comes from world records. A study of individual runners (Blythe & Király, 2016) found a higher median individual exponent of 1.12. If you only have short-race times or have not done much long-distance training, your real marathon time is often slower than predicted.
- Elevation, temperature and how you feel on the day are not taken into account.
Input format and distance standards
Enter time as h:mm:ss (1:05:30) or mm:ss (75:00), and pace as min:sec (5:30). Minutes and seconds after a colon must be 0–59; a single number is rejected. Distance is limited to 400 km, time to 99:59:59 and entered pace to 59:59.
The race buttons use 21.0975 km for a half marathon and 42.195 km for a marathon. One mile is exactly 1.609344 km.