Average car consumption

How do you calculate the average fuel consumption of a car? Newer cars already have an on-board computer that calculates average consumption for you. If you don't have such an on-board computer, or don't trust it for some reason, you can calculate the average consumption yourself.

You'll need two things to do this: measure how far you've driven and how much fuel you've used in that time. The easiest way to do this is to fill up a full tank and start counting your mileage from there. After some time, drive to a petrol station and fill up again. If at this point you have filled up with, say, 40 litres of fuel, this means you have used 40 litres of petrol or diesel since you last filled up. Now see how many kilometres you have driven since you last filled up. That'll be 600 kilometres. Now, if you divide

$$\Large \frac{600\ \mbox{km}}{40\ \mbox{l}}=15\ \mbox{km}/\mbox{l}$$

You've travelled 15 kilometres on one litre of fuel. But it's customary in this country to give the fuel consumption per hundred kilometres. You find this by calculating

$$\Large \frac{100\ \mbox{km}}{15\ \mbox{km}/\mbox{l}}=6{,}666\ \mbox{l}$$

We get a consumption of about six and a half litres per hundred kilometres. You can get the same consumption by another method, namely

$$\Large\frac{40\ \mbox{l}}{600\ \mbox{km}}=0{,}0666\ \mbox{l}/\mbox{km}$$

So you use 0.0666 litres of fuel per kilometre travelled. If we multiply this value by 100, we again get the consumption per hundred kilometres:

$$\Large\frac{40\ \mbox{l}}{600\ \mbox{km}}\cdot100\ \mbox{km}=6{,}666\ \mbox{l}$$