Car fuel consumption calculator

The trip computer shows fuel consumption, but it tends to flatter you. A more accurate method is to fill the tank to the top and reset the trip meter, then at the next fill-up fill it to the top again and see how many litres went in. That is the fuel the car used over the distance the trip meter shows.

How it works

Consumption per 100 km is

$$\text{consumption}=\frac{\text{litres}}{\text{km}}\cdot 100$$

Since the last fill-up we have driven 600 km and added 40 litres. So per kilometre we used

$$\frac{40\text{l}}{600\text{km}}\approx 0.0667\text{l/km}$$

and per hundred kilometres, a hundred times as much:

$$0.0667\cdot 100\approx 6.67\text{l/100 km}$$

Turned round, $600÷40=15$ tells us that we drive 15 km per litre. This is how fuel economy is quoted in the UK and the USA, only in miles per gallon.

A single fill-up can distort the result if the pump clicks off early one time and late the next. A more reliable method is to add up the kilometres and litres over several fill-ups and only then divide. This is explained in more detail in the article on average car fuel consumption. To work out what the whole journey will cost, use the car journey cost calculator.