Fuel Economy Calculator

Work out your car's real fuel economy from the distance driven and the fuel used, and convert freely between MPG (US & UK), litres per 100km and km per litre. Updates as you type.

How it works

• MPG = miles ÷ gallons (UK gallon = 4.546 L, US gallon = 3.785 L — so UK MPG reads higher).
• km/L = kilometres ÷ litres. L/100km = litres ÷ km × 100 (lower is better).
• 1 mile = 1.609 km. The calculator converts your inputs and shows every common measure.
• For accuracy: fill the tank, drive normally, refill, and use the distance and the refill amount.

FAQ

How do I calculate my car's fuel economy?

Divide distance by fuel used. Miles ÷ gallons = MPG; km ÷ litres = km/L; litres ÷ km × 100 = L/100km. The most accurate method is to fill the tank, drive normally, refill, and use the distance covered and the litres or gallons it took to refill.

What is the difference between US MPG and UK MPG?

Different gallons. A UK gallon is ~4.546 L and a US gallon ~3.785 L, so the same real economy shows a higher number in UK MPG. This calculator shows both.

Is a lower or higher L/100km better?

Lower is better for L/100km — less fuel for the same distance. That's the opposite of MPG and km/L, where higher is better. A car at 5 L/100km beats one at 8 L/100km.

How can I improve my fuel economy?

Smooth driving helps most — gentle acceleration, steady speeds, avoiding very high motorway speeds. Keep tyres inflated, remove excess weight and roof racks, service the car, and avoid idling. Real economy is usually 10–20% worse than the official figure.

Want the cost too? Use the fuel cost calculator, or browse all free tools.