Fuel Efficiency Calculator
Enter the miles driven and fuel used from a fill-up to get your true MPG, the equivalent L/100km, and what each mile of driving costs you in fuel.
Where does your car sit? (US averages)
Frequently asked questions
How do I calculate my car’s MPG?
Fill the tank, reset the trip meter, drive normally, then fill up again and note the gallons pumped and miles driven. MPG = miles driven ÷ gallons used. Example: 350 miles on 12.5 gallons = 28 MPG. The calculator above does the division and converts to L/100km at the same time.
Why does my real-world MPG differ from the official rating?
Official EPA/WLTP figures come from standardized lab cycles. Real driving involves cold starts, air conditioning, traffic, hills, load and driving style — typically producing 10–25% lower figures. City stop-and-go driving hurts the most; steady highway cruising usually gets closest to the official number.
Why does the US use MPG while Europe uses L/100km?
They measure opposite things: MPG rewards high numbers (more miles per gallon), while L/100km rewards low numbers (less fuel per fixed distance). L/100km is arguably more intuitive for cost math — you always drive a distance, so fuel-per-distance directly predicts your bill. Note the two scales are inverses, not simple conversions: 40 MPG ≈ 5.9 L/100km, but 20 MPG ≈ 11.8 L/100km.