Measure your car’s fuel economy. This free miles per gallon calculator turns miles driven and fuel used into MPG, with L/100km, km/L and imperial MPG, plus an odometer mode.
Your tank
mi
mi
mi
gal
Fill the tank, drive, then refill. Enter the miles driven (or your odometer readings) and the gallons it took to refill. That gives your real-world MPG.
Miles per gallon
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Enter miles and fuel
MPG (US)
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L / 100 km
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km / L
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MPG (UK / imperial)
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MPG = miles ÷ gallons. The US gallon (3.785 L) is smaller than the UK gallon (4.546 L), so US and imperial MPG differ for the same car — both are shown. Lower L/100km means better efficiency.
Use this free miles per gallon calculator to measure your car’s real fuel economy. Enter the miles driven and the fuel used, and get your MPG plus L/100km and km/L.
What this miles per gallon calculator does
A miles per gallon calculator works out your vehicle’s fuel efficiency from a tank of fuel. Divide the distance by the fuel used and you get MPG — the tool also shows the metric equivalents and imperial MPG.
How MPG is calculated
MPG = miles driven ÷ gallons used
L/100km = 235.21 ÷ MPG (US)
420 miles on 12 gallons is 35 MPG — about 6.7 L/100km or 14.9 km/L.
How to measure your MPG accurately
Fill the tank completely and note the odometer (or reset the trip meter).
Drive normally until you need fuel again.
Refill completely and note the miles driven and the gallons it took.
Enter both — the gallons to refill equal the fuel you used.
US vs UK gallons
A US gallon (3.785 L) is smaller than a UK/imperial gallon (4.546 L), so the same car shows a higher number in imperial MPG. This calculator shows both so you’re never comparing the wrong one.
Good MPG, roughly
US MPG
L/100km
Sense
20
11.8
Thirsty
30
7.8
Average
40
5.9
Efficient
50+
4.7
Very efficient / hybrid
Miles Per Gallon FAQ
How do I calculate miles per gallon?
Divide the miles you drove by the gallons it took to refill. For example, 420 miles on 12 gallons is 35 MPG.
How do I measure MPG accurately?
Fill the tank, note the odometer, drive normally, then fill up again. The gallons to refill are the fuel you used over those miles.
What's the difference between US and UK MPG?
The US gallon is smaller (3.785 L) than the imperial gallon (4.546 L), so imperial MPG is a higher number for the same car. The calculator shows both.
How do I convert MPG to L/100km?
Divide 235.21 by the US MPG. So 35 MPG is about 6.7 L/100km. Lower L/100km means better efficiency.
What is a good MPG?
Roughly: 30 MPG is average, 40 is efficient, and 50+ usually means a hybrid or very economical car. It depends heavily on the vehicle and how you drive.
Is the miles per gallon calculator free?
Yes, this miles per gallon calculator is completely free, needs no sign-up, and gives instant results in your browser.
