Speed, time and distance calculator

Speed, time and distance are linked by a single formula: speed is the distance travelled divided by the time taken. If you drive the 210 km from London to Nottingham in 2 hours, your average speed is 105 km/h. So from any two of these quantities you can always work out the third, simply by rearranging the formula.

Just watch the units. Kilometres divided by hours give km/h, metres divided by seconds give m/s, and you convert one into the other with the number 3.6: 1 m/s = 3.6 km/h. The calculators keep track of this for you, and you can enter the distance and the time in any units.

Speed from distance and time

Distance from speed and time

Time from distance and speed

How it works

All three calculators use the same formula, just rearranged each time:

$$v=\frac{s}{t},s=v\cdot t,t=\frac{s}{v}$$

In the first calculator we travelled 120 km in an hour and a half. Substituting into the formula:

$$v=\frac{120\text{km}}{1.5\text{h}}=80\text{km/h}$$

In metres per second, that is $80÷3.6\approx 22.22\text{m/s}$.

In the second, we drive at 80 km/h for 45 minutes. First we convert the minutes to hours: 45 minutes is three quarters of an hour, so 0.75 h:

$$s=80\text{km/h}\cdot 0.75\text{h}=60\text{km}$$

In the third, we have 300 km of motorway ahead of us and drive at 120 km/h:

$$t=\frac{300\text{km}}{120\text{km/h}}=2.5\text{h}$$

Half an hour is 30 minutes, so the journey takes 2 hours and 30 minutes. A common mistake is to read 2.5 h as “two hours fifty”. The journey actually takes 20 minutes less than that, because an hour has 60 minutes, not 100.

This is the average speed: the calculator does not mind that you sat in a traffic jam for half an hour and then made up the time. You will find more examples with unit conversions in the article How to calculate average speed. For why the average speed for a trip there at 120 km/h and back at 40 km/h is not 80 km/h, see the article on the harmonic mean.