How to use the Gas Mileage Calculator tool
3 simple steps · under a minute
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Fill up and reset
Fill the tank and reset your trip meter.
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Drive, then fill up again
Note the miles driven and how much fuel it took to fill the tank again.
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Read your MPG
See your fuel economy in MPG and L/100 km, and the cost per mile.
About Gas mileage calculator
Gas mileage, or fuel economy, measures how far your car goes on a gallon or litre of fuel. Tracking it helps you spot problems early — a sudden drop can mean low tyre pressure or an engine issue — and shows how much your driving costs. This MPG calculator works it out from the distance you drove and the fuel you used.
For the most accurate result, use the fill-up method: fill the tank, reset the trip meter, drive normally, then fill up again and note the gallons it took. Note that UK gallons are about 20% larger than US gallons, so the same car shows a higher MPG in the UK.
US, UK or metric
MPG with US or UK gallons, or litres per 100 km.
All units at once
See every common measure of fuel economy together.
Cost per mile
Add the fuel price to see what each mile or kilometre costs.
Frequently asked questions
How do I calculate gas mileage?
Divide the miles driven by the gallons of fuel used. 320 miles on 11.5 gallons is 27.8 MPG.
How do I convert MPG to L/100 km?
Divide 235.21 by the US MPG. 27.8 MPG is about 8.5 L/100 km.
Why is UK MPG different from US MPG?
A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres, so UK MPG figures are about 20% higher.
What is good gas mileage?
For a modern petrol car, 30+ MPG (US) is good; hybrids often reach 45–55 MPG.
How can I improve my gas mileage?
Keep tyres properly inflated, drive smoothly, avoid idling, remove extra weight and keep up with servicing.