Free Gas Mileage Calculator
Find your true MPG from your last fill-up, or price a road trip down to the gallon before you leave.
This free gas mileage calculator computes MPG from miles driven and gallons used, estimates trip fuel cost from distance, MPG, and gas price, and shows cost per mile, so you can compare cars and plan road trips on real numbers.
Fill the tank fully both times for an accurate reading.
Estimates for planning. Real MPG varies with speed, load, weather, and driving style.
Email me my results
Get your calculation sent to your inbox, plus occasional tips about our free tools.
How gas mileage math actually works
Miles per gallon is miles driven divided by gallons used. Fill the tank, reset the trip odometer, drive normally, fill again, and divide the trip miles by the gallons the second fill took. That is your real MPG: no dashboard optimism, no EPA estimate.
Trip cost is distance divided by MPG, times gas price. A 600-mile trip in a 30 MPG car at $3.20 a gallon needs 20 gallons and costs $64. The same trip in a 20 MPG SUV costs $96. Fuel is usually the biggest variable cost of a road trip, bigger than tolls for most routes.
Cost per mile is the number that makes car comparisons honest: gas price divided by MPG. At $3.20 and 30 MPG, every mile costs about 10.7 cents in fuel. A car that gets 5 fewer MPG costs you an extra 2.1 cents per mile, which is about $320 a year at 15,000 miles.
Dashboard MPG readouts typically run 1 to 2 MPG optimistic because they estimate from injector data rather than measuring pump gallons. The fill-up method is the ground truth; if your dashboard says 32 and your math says 30, trust the math.
Small driving changes move MPG more than most gadgets: steady highway speed, proper tire pressure, and removing roof racks or excess cargo. Aggressive acceleration and idling are the two biggest fuel wasters in city driving.
Gas mileage questions
How do I calculate my car's gas mileage?
Fill the tank and reset your trip odometer. Drive normally, then fill up again. Divide the trip miles by the gallons the second fill took. That is your true MPG.
How much does a road trip cost in gas?
Divide the trip distance by your MPG to get gallons needed, then multiply by the gas price. A 600-mile trip in a 30 MPG car at $3.20 a gallon costs about $64 in fuel.
Why is my real MPG lower than the EPA rating?
EPA figures come from standardized lab cycles. Real driving with highway speeds, cold starts, short trips, air conditioning, and cargo typically lands 10 to 20 percent lower.
Does premium gas improve mileage?
No. Premium gasoline contains no more energy than regular; it only resists knock in high-compression engines. If your manual says regular, premium buys nothing.