Speed calculator: distance ÷ time
Timed something with the stopwatch? Enter the distance and the time (a stopwatch reading like 12.48 or 1:05.3 works) and get the speed in every common unit. Or solve for distance or time instead.
Speed, distance and time
Speed = distance ÷ time. Everything else is unit conversion: 1 m/s = 3.6 km/h ≈ 2.237 mph, and 1 knot = 1.852 km/h exactly. A sprinter covering 100 m in 10.00 s averages 10 m/s, or 36 km/h.
Measuring speed with a stopwatch
Mark two points a known distance apart, start the stopwatch as the object passes the first and stop it at the second. The longer the distance, the smaller the effect of your reaction time: a 0.2 s timing error is 2% of a 10 s run but 20% of a 1 s run. For a car passing two lamp posts 50 m apart in about 3 s, expect roughly ±7% error from hand timing alone.
| Example | Distance | Time | Average speed |
|---|---|---|---|
| 100 m sprint (elite men) | 100 m | 9.80 | 36.7 km/h |
| Brisk walk | 1 km | 10:00 | 6.0 km/h |
| 5K run | 5 km | 25:00 | 12.0 km/h |
| Swimming 50 m | 50 m | 40.00 | 4.5 km/h |
Questions people ask
How do I calculate speed?
Divide distance by time. 100 m in 12.5 s is 8 m/s; multiply by 3.6 for km/h (28.8 km/h) or by 2.237 for mph (17.9 mph).
How do I convert km/h to mph?
Divide by 1.609344. For example 100 km/h ≈ 62.1 mph.
Can I type a stopwatch reading directly?
Yes. Enter seconds (12.48), minutes and seconds (1:05.3) or hours, minutes and seconds (1:02:00).