Fuel Mileage Calculator
Knowing your real fuel mileage lets you budget trips, compare vehicles, and judge whether efficiency changes are actually working. Enter the miles you drove, the gallons of fuel you used, and the price per gallon. This calculator returns your miles per gallon, gallons used per 100 miles, the fuel cost of the trip, and the fuel cost per mile. For the most accurate MPG, measure tank to tank: fill up, reset the trip meter, drive, and fill up again.
Fuel mileage formula
MPG = miles driven / gallons used
Gallons per 100 miles = 100 * gallons / miles
Trip fuel cost = gallons used * price per gallon
Cost per mile = price per gallon / MPG
MPG is distance per fuel; gallons per 100 miles is fuel per distance. Cost per mile turns your efficiency and fuel price into a running cost for budgeting.
Getting an accurate figure
- Measure tank to tank: fill, reset the trip meter, drive, then refill and record gallons.
- Real-world MPG varies with speed, load, terrain, weather, and tire pressure.
- Gallons per 100 miles compares fuel savings more directly than MPG.
- Cost per mile is handy for trip budgets and mileage reimbursement comparisons.
- Track several tanks to smooth out fill-level and driving variation.
Fuel mileage: frequently asked questions
How do you calculate miles per gallon?
Miles per gallon (MPG) is the distance you drove divided by the fuel you used: MPG = miles driven / gallons used. The most accurate way to measure it is to fill the tank, reset the trip odometer, drive normally, then fill up again and divide the trip miles by the gallons it took to top off. That captures exactly the fuel burned over that distance.
What is cost per mile for fuel?
Fuel cost per mile is the price per gallon divided by your miles per gallon: cost per mile = price per gallon / MPG. It tells you the fuel cost of each mile driven, which is useful for budgeting, comparing vehicles, and estimating the running cost of a trip or a reimbursement rate.
How is gallons per 100 miles different from MPG?
Gallons per 100 miles measures fuel consumed per fixed distance, so lower is better, while MPG measures distance per fixed fuel, so higher is better. Consumption per distance scales linearly with fuel use, which makes it easier to compare savings between two efficiencies than MPG, where equal MPG gains do not mean equal fuel savings.
Why does my real MPG differ from the EPA rating?
The EPA window-sticker figures come from standardised test cycles. Real-world MPG depends on speed, acceleration, terrain, load, weather, tire pressure, and maintenance. Driving style and conditions commonly move actual MPG above or below the rating. Measuring your own tank-to-tank MPG gives the number that applies to how and where you drive.
How can I improve my fuel mileage?
Steady speeds, gentle acceleration and braking, correct tire pressure, removing excess weight and roof loads, and keeping up with maintenance all help. High speeds increase aerodynamic drag sharply, and idling burns fuel for zero miles. Track your MPG over several tanks to see which changes actually move the number for your vehicle.
Official sources
- U.S. Department of Energy and EPA: fueleconomy.gov MPG ratings and tips.
- U.S. Environmental Protection Agency: EPA fuel economy testing.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.