How the calculator works it out
Fuel cost is just gallons burned times the price of a gallon. The gallons come from the distance and your car’s fuel economy.
Miles = one-way distance × 2 for a round trip
Gallons = miles ÷ MPG
Trip cost = gallons × price per gallon
Each person pays = trip cost ÷ people
Worked example: four friends, 240 miles each way
The round trip is 480 miles. At 30 MPG that burns 480 ÷ 30 = 16 gallons. At $4.35 a gallon the fuel costs 16 × 4.35 = $69.60, so each of the four pays $17.40. Every mile costs 4.35 ÷ 30 = 14.5 cents in fuel.
Finding the right numbers
- Distance: use the driving distance from your map app, not the straight-line distance.
- MPG: look up your exact car on fueleconomy.gov, or work out your real figure with the gas mileage calculator. On the EPA label, combined MPG is 55% city and 45% highway.
- Gas price: the EIA weekly gasoline and diesel update publishes U.S., regional and some state averages every Monday. The default here is the U.S. regular average for the week of October 5, 2026.
This is fuel only. Wear and tear, tolls and parking are extra; the IRS business mileage rate, 76 cents a mile from July 1, 2026, is one benchmark for the full cost of running a car. See the mileage reimbursement calculator.
Questions people ask
How do I work out the gas cost of a road trip?
Divide the total miles by your car’s MPG to get gallons, then multiply by the price per gallon. A 480 mile round trip at 30 MPG uses 16 gallons; at $4.35 a gallon that is $69.60.
What MPG should I use?
For a highway trip, use your car’s EPA highway figure or, better, your own logged mileage on a recent highway tank. The combined figure on the window sticker assumes 55% city driving, so it usually understates a long highway run. Roof boxes, a full load and high speeds pull it down.
How should friends split gas money?
The fair split is fuel cost divided by everyone in the car, driver included, which is what this calculator does. Some groups leave the driver out because they supply the car; to do that, enter one fewer person. Tolls and parking are not included.
Does the share link include any personal information?
No. The link holds only the five numbers on the form: distance, one way or round trip, MPG, gas price and number of people. Nothing is saved on our side.
Where does the default gas price come from?
It is the U.S. average retail price for regular gasoline from the Energy Information Administration’s weekly survey, $4.35 for the week of October 5, 2026. Prices change every week and vary a lot by state, so type in what you see at the pump.