The road trip is free. The road trip's fuel is $87.
Use this free gas cost calculator to find the fuel cost of any trip. Enter the distance in miles, your car's MPG, and the price per gallon, and get the total — for road trips, commutes, moving day, or settling who owes what for gas.
Three numbers decide every fuel bill: how far, how thirsty, and how expensive. Only one of them is in the news, and the other two matter more.
What This Gas Cost Calculator Does
- Calculates total fuel cost for a trip from distance, MPG, and gas price
- Works for one-way or round trips (double the distance for round trips)
- Lets you compare vehicles, routes, or the real cost of a long commute
- Gives the number to split with passengers without anyone having to guess
How to Use the Gas Cost Calculator
Inputs:
- Distance — trip miles. Double it for a round trip
- MPG — your car's real-world fuel economy, not the window sticker
- Gas Price — price per gallon
Steps:
- Enter the distance (round trip if that is what you are paying for)
- Enter your MPG — calculate your own as miles driven ÷ gallons filled over a couple of tanks
- Enter the current gas price and click Calculate
- Splitting with passengers? Divide the total by the number of people, driver included
How the Calculation Works
Gallons = Distance ÷ MPG
Trip Cost = Gallons × Price per Gallon
- Real-world MPG runs 10–20% below the EPA sticker in mixed driving, and worse in winter, in traffic, or with a loaded roof rack
- Highway speed matters a lot: most cars lose efficiency above 60 mph, and 75 mph can cost 15–20% more fuel than 65
- Metric conversion: L/100 km → MPG = 235.2 ÷ (L/100 km)
- Fuel is only part of per-mile cost. Including maintenance, tires, and depreciation, the IRS 2025 standard mileage rate is $0.70/mile — for a 300-mile trip that is $210, not $42
Worked Example: 420-mile round trip, 28 MPG, $3.45/gallon
- Gallons = 420 ÷ 28 = 15 gallons
- Cost = 15 × 3.45 = $51.75
- Split four ways: $12.94 each — cheaper than any of them could fly, drive alone, or argue about
- Total ownership cost at $0.70/mile would be $294. Fuel is the visible part of a much larger bill.
Tips (From People Who Have Made These Mistakes)
- Calculate your actual MPG once: fill up, note the odometer, drive normally, fill up again, divide miles by gallons. Most people are 3–5 MPG more optimistic than reality
- Proper tire pressure is worth up to 3% efficiency and costs nothing. Check it monthly
- Fuel apps and warehouse clubs routinely save $0.20–0.40 per gallon — $6 on a 15-gallon fill
- Commuting? Multiply the daily round trip by 250 workdays to see the yearly figure, then look at the commute cost calculator for the time you are also spending
Frequently Asked Questions
How do I calculate gas cost for a trip?
Divide miles by MPG to get gallons, then multiply by the price per gallon. 300 miles ÷ 25 MPG = 12 gallons × $3.50 = $42.
How much gas will I use on a 500-mile trip?
At 25 MPG, 20 gallons. At 35 MPG, 14.3. At 18 MPG, 27.8. MPG matters more than route on any long drive.
How do I split gas money on a road trip?
Total fuel cost divided by everyone in the car, including the driver. For long trips it is fair to add tolls, and some groups add a per-mile amount for wear — the trip cost calculator covers the fuller picture.
How do I calculate my car's MPG?
Fill the tank, reset the trip odometer, drive normally, fill again, then divide miles driven by gallons added. Average two or three tanks for a reliable figure.
Does driving slower save gas?
Usually yes between 55 and 80 mph, where aerodynamic drag dominates — dropping from 75 to 65 typically saves 10–15%. Very slow, stop-and-go driving is worse than steady highway cruising.
Mini Roast Disclaimer
We roast the number, not you. The car gets 28 MPG. The roof box you strapped on gets 22, and it is carrying one folding chair.
Reality Check
Fuel cost is the easy part; it ignores tolls, parking, maintenance, tires, and depreciation, which together roughly quadruple the true per-mile cost. Real MPG also varies with terrain, load, weather, and speed, so treat the result as a solid estimate rather than an exact receipt.