What Car? Q&A - How do I work out fuel consumption?

Q: How do I work out the fuel consumption of my car? I run a diesel Peugeot 106 and it seems to hardly ever require a trip to the filling station. I would like to work out a figure to confirm its seemingly infinite fuel economy.
Ruth Corfield

A: Next time you fill your car, make sure you brim the tank, or brim it to a specified number of clicks, and then record the mileage or reset the trip meter if you have one. When the tank is reaching empty, refill it in the same way, noting the number of litres and the mileage figure on your odometer.

Convert the litres into gallons – there are 4.546 litres in one gallon (so divide litres by 4.546). If you do not have a trip meter, simply subtract the first odometer reading from the second and divide this figure by the number of gallons.

This final figure is the average number of miles that your car will travel on one gallon of fuel.

If your 106 is not returning at least 55mpg, we would advise that you ensure the air filter is clean, the injectors are working properly and that your tyres are inflated to the specified pressures.