Gallons used formula
Gallons used = miles driven / MPG
A 300-mile drive in a 30 MPG vehicle uses about 10 gallons. If gas is $3.60 per gallon, the fuel cost is about $36.
Fuel use
Gas usage calculator
Calculate how many gallons a drive will use from distance and MPG. Add gas price when you also want fuel cost and cost per mile.
Cost per mile formula
Fuel cost per mile = gas price / MPG
At $3.60 per gallon and 30 MPG, the fuel-only cost is about $0.12 per mile. Tolls, parking, maintenance, and depreciation are separate costs.
When to use gas usage instead of trip cost
Use gas usage when you mainly need gallons: estimating fuel stops, comparing MPG assumptions, or checking whether your dashboard average seems reasonable. Use trip cost when you need dollars for a budget.
For mixed city and highway driving, use combined MPG. For a highway-only road trip, highway MPG may be closer, but it still depends on speed, weather, traffic, and cargo weight.
Convert metric fuel use correctly
Miles per gallon gets better as the number rises, while liters per 100 kilometers gets better as the number falls. They are inverse measures, so do not enter an L/100 km value in an MPG field. The inline calculator switches the formula and returns both gallons and liters.
Fuel cost uses the entered price per U.S. gallon. If the posted station price is per liter, multiply liters used by that per-liter price instead of using the dollar output. For fuel-stop planning, keep a reserve and use the vehicle's usable tank capacity rather than assuming every stated gallon is available.
Gas usage FAQ
Can I use kilometers?
Yes. Switch the inline calculator to kilometers and L/100 km. It returns both liters and U.S. gallons.
Why did I use more gas than estimated?
Actual use can rise with cold weather, high speed, hills, roof racks, idling, traffic, tire pressure, and extra cargo.