How to estimate fuel cost
Divide total miles by the vehicle’s miles per gallon to estimate gallons used. Multiply gallons by the expected price per gallon. For a round trip, make sure the distance field already includes both directions.
Choosing a realistic MPG
Published fuel economy is a useful starting point, but speed, traffic, weather, elevation, tire pressure, cargo, and driving style affect real use. Your recent trip-computer average may be more realistic for planning.
Allowing for uncertainty
Fuel prices can vary along a route. Consider adding a small buffer for detours, idling, or price changes. Tolls, parking, maintenance, and vehicle depreciation are not included.
Work a complete trip example
For 480 total miles at 30 mpg, estimated fuel is 480 ÷ 30 = 16 US gallons. At $3.50 per gallon, the fuel estimate is $56. Split equally among four travelers, that is $14 each. Reverse-check by multiplying 16 gallons by 30 mpg to recover 480 miles. If 480 describes only the outbound leg of a round trip, enter 960 miles instead; forgetting the return distance is a larger error than rounding the cents.
Build a low and high scenario
Use recent observed mpg for similar driving when available. For uncertainty, calculate once with a lower efficiency and higher fuel price, then again with an optimistic pair. Keep route distance, mpg source, price date, and excluded costs with the estimate. A fair cost-sharing agreement may include only fuel or may also include tolls and parking; state that choice before dividing. For mixed units, convert L/100 km or km/L with the fuel-economy converter before using this US-unit calculator.
This version uses miles, US gallons, and US dollars. Results are estimates, not guarantees.