Fuel Cost Calculator - Gas Cost for Any Road Trip

The formula

Fuel cost = (miles ÷ MPG) × price per gallon. The first part gives gallons burned; the second turns gallons into dollars. Cost per mile is simply price ÷ MPG, which is handy for comparing cars or deciding whether a detour to cheaper gas is worth it.

The calculator adds three practical extras: a round-trip toggle that doubles the distance, a passenger split, and a line showing what the trip would cost in a car that gets 5 MPG more, so you can see what efficiency is worth on your actual route.

Worked example: a weekend road trip

Say the drive is 450 miles one way, a little less than Chicago to Nashville. In a 25 MPG car with gas at $3.40, one way uses 18 gallons and costs $61.20. Tick round trip and it becomes 900 miles, 36 gallons, and $122.40.

Split four ways, each person owes $30.60. In a 30 MPG car, the round trip drops to $102, or $25.50 each. Fuel runs 13.6 cents per mile in the 25 MPG car and 11.3 cents in the 30 MPG car.

Now scale to a year. Driving 12,000 miles in a 25 MPG car at $3.40 costs $1,632 in gas. In a 35 MPG car, $1,166. That $466-a-year gap is a useful number when you are shopping for a car or weighing a hybrid premium.

Getting the inputs right

MPG: the EPA rating on the window sticker and fueleconomy.gov is the fairest starting point. Use highway MPG for interstate trips and combined MPG for mixed driving. For your real number, fill the tank, reset the trip meter, drive normally, refill, and divide miles by gallons added. Most dashboards' MPG readouts run a little optimistic.

Gas price: the U.S. Energy Information Administration publishes weekly national and regional averages. Prices vary a lot by region: California regularly runs more than $1 a gallon above the Gulf Coast. For a long trip, use an average of the states you will cross.

Distance: use the route your map app suggests, not straight-line distance, and add 5 to 10% for detours, food stops, and driving around at the destination.

What lowers real-world MPG

Speed is the biggest factor you control. Most cars are most efficient somewhere around 50 mph, and economy falls quickly above that. FuelEconomy.gov's guidance is that every 5 mph over 50 is like paying noticeably more per gallon, and going 80 instead of 65 can cut highway MPG by 15% or more.

Other drains: roof racks and cargo boxes (up to about 25% at interstate speeds for a loaded rooftop box), cold weather (10 to 20% for short trips in freezing temperatures, more for hybrids), underinflated tires, heavy loads, and aggressive acceleration. Air conditioning costs a few percent; open windows at highway speed cost about the same in drag.

Fuel cost vs total cost of driving

Gas is only part of what a trip costs. The IRS standard mileage rate, which is meant to cover fuel plus depreciation, insurance, maintenance, and tires, was 70 cents per mile for business driving in 2025, about five times the fuel-only figure in the example above. If you are reimbursing someone for using their car, the IRS rate is the fairer number. If you are splitting gas with friends, fuel cost is the norm.

For an electric car, replace MPG and gas price with miles per kWh and electricity price. At 3.5 miles per kWh and 17 cents per kWh at home, 450 miles costs about $21.86. Public DC fast charging often costs two to three times as much per kWh.

Common mistakes

Forgetting the return leg. A one-way estimate for a round trip halves the budget. Use the round-trip box.

Using city MPG for highway trips, or the other way around. The gap is often 20 to 30% for gas cars, and it runs the other way for many hybrids, which do better in the city.

Leaving out tolls and parking. They can rival fuel on some Northeast routes. Add them separately and split them the same way.