Gas Mileage Calculator
Work out your real fuel economy from the distance you drove and the fuel you used. Get MPG (US and UK), km per liter and liters per 100 km — the honest number, not the sticker.
Fuel economy
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How to Measure Gas Mileage
The reliable method is a tank-to-tank test:
- Fill the tank and reset your trip meter (or note the odometer).
- Drive normally until you need fuel again.
- Fill up and note how many gallons or liters it took.
- Divide the distance by the fuel used.
MPG = Miles driven ÷ Gallons used L/100km = Liters used ÷ Distance (km) × 100
US mpg vs. UK mpg
They aren’t the same figure. A UK (imperial) gallon is about 20% larger than a US gallon (4.546 L vs. 3.785 L), so the same car scores a higher mpg number in the UK. Always check which gallon a quoted figure uses — this calculator shows both.
Lower L/100km Is Better
MPG and km/L go up as a car gets more efficient, but L/100km goes down — it measures fuel consumed, not distance covered. A car at 5 L/100km sips less than one at 8 L/100km.
Turn It Into a Trip Cost
Once you know your economy, estimate what a journey will cost with the fuel cost calculator. Measure the driving distance first with the driving distance tool so the numbers reflect the real route.
Get Distance Measure
Download Distance Measure for iOS and start measuring in seconds.
