How to use the fuel cost calculator
- Enter the trip distance one way and choose miles or kilometers.
- Enter your vehicle's fuel economy in mpg (US), mpg (UK), L/100 km or km/L.
- Enter the fuel price and whether it's per US gallon, per UK gallon or per liter.
- Tick round trip to count the drive back.
- Enter how many people are sharing the cost.
- Read the total, the fuel needed and the cost per person, plus a table showing what the trip costs if prices move.
The units don't have to match. You can enter miles, mpg (UK) and a price per liter, as drivers in the UK do, and the calculator converts between them.
How fuel cost is calculated
A round trip doubles the distance. The calculator uses exact unit definitions: 1 mile is 1.609344 km, a US gallon is 3.785411784 liters and a UK (imperial) gallon is 4.54609 liters. That matters when you mix units, because a UK gallon is about 20% bigger than a US gallon.
Worked example
The defaults are a 350-mile trip in a car that gets 25 mpg (US), with fuel at $3.50 a gallon:
- Fuel used: 350 ÷ 25 = 14 US gallons (53.0 liters)
- Fuel cost: 14 × $3.50 = $49.00
- Cost per mile: $49.00 ÷ 350 = $0.14
Tick round trip and the distance becomes 700 miles, so the fuel is 28 gallons and the cost is $98.00. Split between two people, that's $49.00 each. In metric, a 500 km trip at 7 L/100 km uses 35 liters, which costs $63.00 at $1.80 a liter.
What a 100-mile drive costs
At $3.50 per US gallon:
| Fuel economy | Fuel used | Cost per 100 miles |
|---|---|---|
| 15 mpg | 6.67 gal | $23.33 |
| 20 mpg | 5.00 gal | $17.50 |
| 25 mpg | 4.00 gal | $14.00 |
| 30 mpg | 3.33 gal | $11.67 |
| 40 mpg | 2.50 gal | $8.75 |
| 50 mpg | 2.00 gal | $7.00 |
Going from 20 to 25 mpg saves more per mile than going from 40 to 50 mpg, because fuel used depends on 1 ÷ mpg. That's why L/100 km, which measures fuel per distance directly, makes comparisons between cars easier.
Getting a realistic estimate
Use the fuel economy you actually get, not the best figure on the window sticker. The gas mileage calculator works it out from two fill-ups. Highway trips at steady speed usually do better than town driving, while roof boxes, towing, heavy loads, strong headwinds and high speeds all push fuel use up. Prices vary between stations and states, so on a long trip you may want to use an average of the prices along the route. The official ratings for most US models are on fueleconomy.gov.
Frequently asked questions
How do I calculate gas money for a trip?
Divide the round-trip distance by your car's mpg to get gallons, then multiply by the price per gallon. A 350-mile trip each way at 25 mpg and $3.50 a gallon uses 28 gallons for $98. Divide by the number of riders to split it fairly.
Should passengers pay for more than fuel?
That's up to you. Fuel is the main cost of a single trip, but tolls, parking and wear on the car add to it. If you want to cover the full cost of driving, the IRS standard mileage rate is a common benchmark; see the mileage calculator.
How do I convert L/100 km to mpg?
Divide 235.215 by the L/100 km figure to get US mpg, or 282.481 for UK mpg. A car using 7 L/100 km gets 235.215 ÷ 7 = 33.6 mpg (US). You can enter either unit here without converting first.
Does the calculator work for diesel or electric cars?
It works for any liquid fuel, including diesel, as long as you enter that fuel's price and your car's economy on it. For an electric car, use an EV charging cost estimate based on kWh instead, since electricity isn't sold by the gallon or liter.
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