Fuel Cost Calculator

Miles per gallon and litres per 100 km are inversely related, not proportional — halving the mpg doubles the fuel used. Pick the unit your car actually shows and let the calculator convert; converting by hand is where this goes wrong.

What a trip costs in fuel is the one number that makes routes, cars and pump prices comparable, and it comes out of three inputs: how far you drive, how much the car uses, and what the fuel costs. The page opens on a 450 km one-way trip at 7 litres per 100 km — that is 31.5 litres — and at 1.75 per litre the trip costs 55.13. Consumption may be entered in whichever unit the car actually shows. Litres per 100 km is the reference; miles per gallon and kilometres per litre are distance per volume and so convert inversely rather than linearly: 235.215 divided by the US mpg figure, 282.481 for imperial gallons, and 100 divided by the km/l figure. The calculator works from the exact definitions of the mile and both gallons instead of those rounded constants. The there-and-back option doubles the distance before anything else runs, so only the one-way leg belongs in the distance field. What the total does not contain is everything about driving that is not fuel — tolls, wear and the car itself are all outside it, and so is any split between passengers: this is the cost of the tank, not a cost per head. The limitation that matters most sits in the consumption figure. A manufacturer's number, city traffic or a loaded car all move real consumption, and the cost moves with it in direct proportion.