Fuel Cost Calculator
Works out what a journey costs in fuel. Enter your economy in whatever unit your car displays and the price in whatever unit the pump quotes — the two do not have to match.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
cost = (distance ÷ economy) × fuel price
Everything is normalised to kilometres per litre and price per litre first, which is why you can mix mpg with a per-litre price or km/L with a per-gallon price without converting anything yourself.
What to watch out for
Three things worth knowing about the number this gives you:
- Real economy is not the sticker figure. Manufacturer figures are laboratory results. Most cars return 10–20% worse in ordinary driving, and short cold journeys can be far worse than that.
- Speed costs more than anything else. Aerodynamic drag rises with the square of speed, so 80 mph uses roughly 25% more fuel than 65 mph over the same distance.
- The cost-per-mile figure is the useful one. It is what lets you compare a journey against a train fare, or one car against another, without doing the arithmetic again.
Frequently Asked Questions
How do I work out fuel cost for a journey?
Divide the distance by your fuel economy to get the fuel used, then multiply by the price. This calculator handles the unit conversions so mpg and per-litre pricing can be mixed freely.
What does it cost to drive 100 miles?
At 35 mpg (US) and $3.50 a gallon, about $10. At 45 mpg (imperial) and £1.45 a litre, about £11.60. The calculator gives cost per mile so you can scale any distance.
Should I use the car computer economy or the sticker figure?
The car computer, and even then treat it as optimistic — trip computers commonly read 3–5% better than a brim-to-brim measurement. For real accuracy, fill up, drive, fill up again and divide.
Does the calculator handle US and imperial gallons?
Yes, separately. An imperial gallon is 4.546 litres against the US gallon at 3.785, so 40 mpg imperial is only 33.3 mpg US for the same car.