Speed calculator
Enter two of speed, distance and time, get the third.
How do I calculate speed?
Speed = distance ÷ time. Usain Bolt's 100 m world record of 9.58 seconds is 100 ÷ 9.58 = 10.44 m/s — 37.6 km/h or 23.4 mph on average.
How do I find distance or time?
Distance = speed × time; time = distance ÷ speed. 60 mph for 2 hours is 120 miles; 120 miles at 60 mph takes 2 hours.
How do I convert m/s to km/h or mph?
Multiply m/s by 3.6 for km/h or by 2.237 for mph. 10 m/s is 36 km/h and 22.4 mph.
Is this average speed?
Yes — total distance over total time. Speed at any moment can be higher or lower.
Speed or velocity?
Speed is how fast; velocity also has a direction. For motion in a straight line one way, they are the same number.
How long does a trip take at a given speed?
Time = distance ÷ speed. At a steady 65 mph, 300 miles takes 4.62 hours, which is 4 h 37 min. Real trips take longer, because stops, traffic and slower stretches pull the average speed below the cruising speed.
Why is my average speed not the average of my two speeds?
Because you spend more time at the slow speed. Drive 60 miles at 60 mph (1 hour) and another 60 miles at 30 mph (2 hours), and the average is 120 miles ÷ 3 hours = 40 mph, not 45. Always divide the total distance by the total time.
How fast is a four-minute mile?
One mile is 1,609.344 m, so 1,609.344 m in 240 s is 6.71 m/s, or 24.14 km/h and 15.00 mph on average.
The formula and what it assumes
Average speed is the total distance traveled divided by the elapsed time, v = d ÷ t (OpenStax University Physics, Volume 1, section 3.2, Eq. 3.5); rearranged, d = v × t and t = d ÷ v. Speed is a scalar with no direction, and instantaneous speed is the magnitude of the velocity (Eq. 3.6). The calculator gives the average over the whole trip, so enter the full path length and the full time, stops included. It converts to meters and seconds first (1 mph = 0.44704 m/s, 1 km/h = 1/3.6 m/s) and then shows m/s, km/h, mph and ft/s.
Worked example: a 10 km run in 52 minutes 30 seconds
The time is 52.5 min × 60 = 3,150 s, because 30 s is half a minute. Speed = 10,000 m ÷ 3,150 s = 3.175 m/s, which is 11.43 km/h, 7.10 mph or 10.42 ft/s. The pace is 5.25 minutes per kilometer, or 8.45 minutes per mile (about 8:27); the pace calculator gives it directly.
Common mistakes
Writing 52 minutes 30 seconds as 52.30 minutes is the usual slip: minutes are not decimal, and 52.30 min is really 52 min 18 s. Mixing units in one problem, such as kilometers with a time in hours but a speed in mph, gives a number that fits none of them; pick the units in the menus and let the calculator convert. And remember that speed counts the whole path: a round trip ends where it began, so the average velocity is zero (OpenStax, section 3.2), but the average speed is not.
Sources: OpenStax University Physics, Volume 1, sections 3.1 (distance traveled and displacement) and 3.2 (average and instantaneous speed, Eq. 3.5–3.6); NIST SP 811, Appendix B.8: 1 mph = 0.44704 m/s and 1 mile = 1.609344 km, both exact. Related: acceleration calculator, kinematics calculator, pace calculator and stopping distance calculator.