Work out how much gas a trip will use and what it'll cost, there and back, and each person's share.
How trip fuel cost is calculated
Gallons = miles ÷ MPG · Cost = gallons × price per gallon
Liters = km × L/100 km ÷ 100 · Cost = liters × price per liter
Per person = cost ÷ people
Worked example
A 300-mile drive in a car that gets 25 MPG uses 300 ÷ 25 = 12 gallons. At $3.50 a gallon that's 12 × 3.50 = $42. There and back is $84, or $21 each for four people.
In metric: 500 km at 6.5 L/100 km uses 500 × 6.5 ÷ 100 = 32.5 liters, which costs $58.50 at $1.80 a liter.
Getting a realistic number
- Use your car's real-world MPG. The gas mileage calculator works it out from a fill-up.
- Highway MPG is usually better than city MPG. Speed, heavy loads, roof boxes, towing, cold weather and air conditioning all lower it.
- Gas prices vary by state and even by station, so use what you see on your route.
- This is fuel only. Tolls, parking, wear and tear, and insurance aren't included.
Sources
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- 300 miles at 25 MPG and $3.50 = 12 gallons, $42 ✓
- Round trip split 4 ways: $84 total, $21 each ✓
- 500 km at 6.5 L/100 km and $1.80/L = 32.5 L, $58.50 ✓
- Edge: 0 MPG is rejected ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
How do I calculate gas cost for a trip?
Divide the distance by your car's MPG to get gallons, then multiply by the price per gallon. 450 miles at 30 MPG and $3.40 is 15 gallons, or $51.
How do I split gas money with friends?
Work out the total fuel cost for the whole trip, including the drive back, and divide by the number of people. Choose Round trip and enter the number of people above.
How do I convert MPG to L/100 km?
Divide 235.215 by the MPG. 25 MPG is about 9.41 L/100 km.
Does driving faster use more gas?
Usually, yes. Most cars are most efficient at moderate speeds, and fuel economy drops quickly at highway speeds above about 50 mph, according to fueleconomy.gov.