Calculate the number of kilometres per litre of fuel.

The easiest way to calculate how much fuel you use travelling a certain distance is to fill up your tank write down the kilometres from your odometer. Next, fill up, look again at your odometer and subtract the first odometer reading from the second one. This calculation will give you the distance travelled by car between fill-ups. Divide this amount by the number of litres it took to fill up your tank at the second fill-up.

distance ÷ fuel = kilometres per litre

Example Calculation

Fill up your tank and look at your car's odometer.
First odometer reading = 098456.7 km

The second fill-up can be any time after the starting one, but if you are trying to figure out how many kilometres per litre, wait with your next fill-up till your tank is closer to being empty for a more accurate result.

At your next fill-up, your odometer reading is 099016.4 km, and it took 60.6 litres to fill up your tank.

Subtract the first reading from the second to get the distance;

099016.4 - 098456.7 = 559.7

Between fill-ups, you travelled a distance of 559.7 kilometres

Divide the distance by the amount of gas it took to fill up the second time;

559.7 ÷ 60.6 = 9.235973597359736 = 9.24 (rounded to 2 digits)

You get an average of 9.24 kilometres per one litre of fuel.