Global Fuel CalculatorGas mileage and fuel cost calculator for the United States
Fuel economy in the United States is measured in miles per gallon, and the gallon in question is the US liquid gallon of 3.785411784 litres — not the larger imperial gallon still used in the UK. That distinction matters: the same vehicle reads roughly twenty percent higher in imperial MPG than in US MPG, which is why UK car reviews always look surprisingly economical to an American reader. This calculator is locked to US gallons throughout.
Enter the miles from your trip odometer, the gallons you pumped, and the price per gallon from the receipt. You get your MPG, your cost per mile, and an optional estimate for an upcoming trip.
If you would rather work in litres — because you are comparing against an imported specification, or you drove in Canada last week — switch the volume selector and the calculator converts for you. The L/100km equivalent is shown alongside every result, so a European figure and an American one can be compared without doing the arithmetic yourself.
Work out your numbers
Indicative starting price only, last reviewed 2026-01. Enter your own pump price for an accurate result.
How fuel economy is measured here
United States works in miles for distance and US gallons for fuel, with economy normally quoted as MPG (US). The calculator above is set that way by default, and the unit selectors let you switch if you need a different basis.
| Unit | Typical local figure |
|---|---|
| L/100km | 8.00 |
| km/L | 12.50 |
| MPG (US) | 29.40 |
| MPG (imperial) | 35.31 |
Local context
Gas is sold by the US gallon with prices displayed to three decimal places — the familiar nine-tenths of a cent on the end. Regular, mid-grade and premium differ in octane rating rather than energy content, so paying for premium in a vehicle that does not require it will not improve your MPG.
State taxes cause wide price variation, with California typically well above the national average and the Gulf states well below. Highway MPG normally exceeds city MPG by a substantial margin, which is why the EPA publishes both figures plus a combined estimate.
Common questions
How do I calculate MPG by hand?
Fill the tank, reset the trip odometer, drive, then refill. Divide the miles driven by the gallons it took to refill. If your trip odometer showed 312 miles and the pump delivered 11.4 gallons, your MPG is 312 divided by 11.4, which is about 27.4.
Is a US gallon the same as a UK gallon?
No, and the difference is large. A US gallon is 3.785 litres while an imperial gallon is 4.546 litres, about twenty percent bigger. A car rated at 30 MPG in the US would be quoted as roughly 36 MPG in the UK for identical real-world consumption. This calculator uses US gallons only.
Why is my real MPG below the EPA sticker number?
EPA figures come from standardized dynamometer cycles. Short trips with a cold engine, heavy air-conditioning use, highway speeds above about 65 mph, roof racks and a loaded vehicle all push real consumption above the test figure. Falling ten to fifteen percent short of the sticker is common.
Does premium gas improve fuel economy?
Not in a vehicle designed for regular. Octane rating measures resistance to pre-ignition, not energy content, so unless your engine is tuned to take advantage of higher octane you are paying more per gallon for the same number of miles.
How do I estimate the gas cost of a road trip?
Establish your MPG from a recent fill-up, enter the current price per gallon, then put your planned route distance in the trip field. The calculator returns both the gallons needed and the dollar cost for that distance.
What does L/100km mean on imported specifications?
It is litres consumed per 100 kilometres, the standard used in Europe and Canada. Unlike MPG, a lower number is better. This calculator shows the L/100km equivalent alongside your MPG so you can compare directly with imported figures.