How to use the average speed calculator
- Choose miles and mph or kilometers and km/h.
- For each leg, enter any two of the distance, the time in minutes and the speed. The page works out the third.
- Add a row for each leg of the trip.
- Read the average speed for the whole trip, the total distance and time, and a table of the legs.
Formula
time = distance / speed
distance = speed x time
speed = distance / time
average speed = total distance / total time
The average speed is not the plain average of the leg speeds unless every leg takes the same time.
Three legs of a drive
Leg 1 is 60 miles at 40 mph, which takes 1.5 hours. Leg 2 is 90 minutes at 60 mph, which covers 90 miles. Leg 3 is 30 miles in 40 minutes, which is 45 mph. The total is 180 miles in 3 hours 40 minutes, so the average speed is 180 / 3.667 = 49.09 mph, while the plain average of the three speeds is 48.33 mph.
On a round trip of 60 kilometers each way at 30 and 60 km/h, the times are 2 hours and 1 hour, so 120 km takes 3 hours and the average speed is 40 km/h, not the 45 km/h you get by averaging 30 and 60.
Why the plain average is wrong
A slower leg takes longer, so it counts for more of the trip. Averaging the speeds treats every leg as if it lasted the same time. The right way is to add the distances and the times separately and divide. The page shows the plain average as well so you can see the difference.
Stops and delays
Average speed is based only on the time you enter. To include a rest stop or traffic, add it as a leg with a short distance and its time, or include the delay in the time of a leg. The result then becomes an average over the whole journey rather than only the time you were moving.
Related travel tools
Plan running and cycling times with the Pace Calculator, cost a drive with the Fuel Cost Calculator, check the range of a tank with the Distance on a Tank Calculator, and check your gauge with the Speedometer Error Calculator.
Assumptions and limits
- Each leg has a constant speed.
- Distances are in the same unit for all legs.
- Time is entered in minutes and shown in hours, minutes and seconds.
- Stops are included only when you add them as legs or in leg times.
Frequently asked questions
How do you find average speed with different speeds?
Divide the total distance by the total time. 180 miles in 3 hours 40 minutes is 49.09 mph, which is not the plain average of the leg speeds.
What is the average speed if I go 30 one way and 60 back?
It is 40, not 45. The slower trip takes twice as long, so over equal distances the average is the harmonic mean, 2 x 30 x 60 / (30 + 60) = 40.
What if I know the distance and time but not the speed?
Enter those two and leave the speed blank. The page computes the speed as the distance divided by the time.
Why does each leg need exactly two values?
Distance, time and speed depend on each other, so two determine the third. Entering all three could contradict, and entering one leaves the leg unknown.