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.
Gas usage FAQ
Can I use kilometers?
The main calculator includes a distance unit selector. You can enter kilometers there and convert the result into fuel cost.
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.