Speed, Distance and Time Calculator
Find the speed, the distance or the time from the other two, in km/h, mph or m/s. The steps show which formula to use, how to write the time in hours, and how to turn a decimal of an hour back into minutes and seconds.
Speed
60 km/h
Covering 150 km in 2 h 30 min is a speed of 60 km/h.
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Why does this work?
All steps as text
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The three formulas, and the triangle
Speed is how far you go in each unit of time, so the three are linked by one rule, written three ways:
- Speed = distance ÷ time. 150 km in 2 h 30 min is 150 ÷ 2.5 = 60 km/h.
- Distance = speed × time. 45 minutes at 60 mph is 60 × 0.75 = 45 miles.
- Time = distance ÷ speed. 200 km at 90 km/h takes 200 ÷ 90 = 2 2/9 hours.
To remember them, draw a triangle with D at the top and S and T along the bottom. Cover the one you want: what is left is the formula. D over T means divide, and S next to T means multiply.
Writing the time in hours, and back again
With a speed in km/h or mph, the time has to be in hours. Divide the minutes by 60: 45 min is 0.75 hours and 2 h 30 min is 2.5 hours. Some don’t give a short decimal: 50 min is 5/6 of an hour, so keep the fraction for an exact answer.
Going back, the whole number is the hours and the part after it, times 60, is the minutes. For 2 2/9 hours: 2 hours, and 2/9 × 60 = 13 1/3 minutes; the 1/3 of a minute is 20 seconds. So 200 km at 90 km/h takes 2 h 13 min 20 s. Note that 2.2 hours is not 2 h 20 min: it is 2 h 12 min.
Changing the units
The distance and the speed have to use the same length: miles with mph, kilometres with km/h. These factors are exact:
- km/h to m/s: divide by 3.6, because 1 km/h is 1,000 m in 3,600 s. 90 km/h is 25 m/s; m/s to km/h is × 3.6.
- mph to km/h: multiply by 1.609344, the kilometres in a mile. 70 mph ≈ 112.65 km/h, and 100 km/h ≈ 62.14 mph.
- mph to m/s: multiply by 0.44704. 60 mph is 26.8224 m/s.
Common speeds in each unit
| Example | km/h | mph | m/s |
|---|---|---|---|
| Walking | 5 | 3.11 | 1.39 |
| Running a 5-minute km | 12 | 7.46 | 3.33 |
| Cycling | 20 | 12.43 | 5.56 |
| Driving in town | 50 | 31.07 | 13.89 |
| Main road | 100 | 62.14 | 27.78 |
| UK motorway limit | 112.65 | 70 | 31.29 |
| Sound in air at 20 °C | 1,235 | 767 | 343 |
Average speed for a whole trip
Average speed is the total distance ÷ the total time, not the average of the speeds. Drive 60 km at 30 km/h (2 hours) and come back at 60 km/h (1 hour): that is 120 km in 3 hours, an average of 40 km/h, not 45. The slow part lasts longer, so it counts for more.
Pace for running and walking
Runners often use pace, the time for each kilometre or mile, which is speed turned upside down. At 12 km/h a kilometre takes 60 ÷ 12 = 5 minutes; at 10 km/h it takes 6 minutes. The calculator shows the pace per km and per mile under every answer.
Questions
How do I calculate speed?
Divide the distance by the time. Covering 150 km in 2.5 hours is 150 ÷ 2.5 = 60 km/h. Write the time in hours for km/h or mph, and in seconds for m/s.
How long will a trip take?
Divide the distance by the speed: 300 miles at 60 mph takes 5 hours. That assumes a steady average speed with no stops, so add time for breaks and traffic.
How do I convert km/h to m/s?
Divide by 3.6: 72 km/h is 20 m/s. To go from m/s to km/h, multiply by 3.6.
What is the difference between speed and velocity?
Velocity is speed in a given direction. For a trip in a straight line one way they are the same number; the formulas here use speed.
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