Fuel cost calculator

How do I calculate the gas cost of a trip?

Divide the distance by your mpg to get gallons, then multiply by the price per gallon. 300 miles at 30 mpg is 10 gallons; at $3.50 a gallon that is $35 — or $70 for the round trip.

What mpg should I use?

Your own from a recent fill-up (the gas mileage calculator works it out), or the EPA combined figure for your car on fueleconomy.gov. Use the highway figure for long interstate trips.

How do I split gas money with passengers?

Divide the total by the number of people: a $70 round trip shared by 2 is $35 each. Enter the number of people and the calculator splits it.

How much does 100 miles of driving cost?

At 25 mpg and $3.50 a gallon: 100 ÷ 25 = 4 gallons × $3.50 = $14. At 40 mpg it is $8.75.

Does it include tolls and wear?

No — only fuel. For the full cost of driving, the IRS standard mileage rate is a common benchmark; it includes depreciation, maintenance and insurance, not just gas.

How much more fuel does a faster speed use?

The Department of Energy’s fueleconomy.gov says gas mileage usually decreases rapidly at speeds above roughly 50 mph, so a trip at 75 mph burns noticeably more fuel per mile than the same trip at 60 mph. For a long highway trip, use a highway mpg from your own fill-ups rather than the combined figure.

Can I use this for a vehicle that is not a gas car?

Yes, if you can express the economy as distance per unit of fuel and give the price for the same unit: diesel works the same way, and for an electric car you would use miles per kWh with the price per kWh. For a direct comparison use the EV vs gas calculator.

The formula

Fuel used = distance ÷ fuel economy, and cost = fuel used × price per gallon. A round trip doubles the distance. Splitting the cost divides it by the number of people, which assumes everyone pays an equal share; it does not include tolls, parking or the wear on the car. Fuel economy is in miles per gallon, so the higher the number, the less fuel each mile takes.

Worked example: a 450-mile trip each way

Take a 450-mile one-way trip, 900 miles round trip, in a car that gets 28 mpg with gas at $3.40 a gallon. Fuel used is 900 ÷ 28 = 32.14 gallons, so the fuel costs 32.14 × $3.40 = $109.29, or $36.43 each for three people. That is $0.121 per mile. If the highway figure turns out to be 24 mpg instead, the same trip burns 37.50 gallons and costs $127.50, which is $18.21 more, so the mpg you enter matters as much as the price.

Common mistakes

Using the sticker’s city or combined mpg for a highway-heavy trip, or the reverse, is the most common source of error, followed by forgetting that gas prices change along the route. Mixing units also bites: a price per liter with mpg gives nonsense, so convert the price to dollars per gallon first (a US gallon is 3.785 liters). Finally, “round trip” doubles the distance for you; entering the round-trip distance and leaving that option on counts the return leg twice.

Sources: speed and fuel economy — U.S. Department of Energy, fueleconomy.gov (“Driving More Efficiently”); the US gallon is defined as exactly 3.785411784 liters (NIST SP 811). Related: gas mileage calculator, mileage reimbursement calculator, EV vs gas calculator and driving CO₂ calculator.