Gas Cost Calculator (Trip Fuel Cost)
Enter the distance, your car’s MPG, and the local gas price. Get the fuel cost for the trip, round-trip, and split between passengers.
| Gallons needed | — |
| Cost per mile | — |
| Per person | — |
The trip fuel formula
Cost = Distance ÷ MPG × Price per gallon
A 500-mile round trip in a 28 MPG car at $3.40/gallon: 17.9 gallons, about $61 — roughly 12 cents per mile of fuel. Split among three passengers, $20 each.
Fuel is less than half the real driving cost
The IRS mileage rate (~65–70¢/mile) prices the full cost of driving — depreciation, tires, maintenance, insurance — while fuel alone is usually 12–18¢/mile. Charging passengers fuel-only is generous; the fair full-cost share for a 500-mile trip is closer to $110/person among three, not $20. For daily commuting math, use the commute cost calculator.
Cheap ways to move the number
- Speed: most cars lose ~15–25% efficiency at 80 mph vs 65 mph — on the example trip that is about $12 for arriving 40 minutes earlier.
- Tires and weight: underinflated tires and a loaded roof rack each cost several percent.
- Apps for cheap stations: a 30¢/gallon spread on 18 gallons is $5.40 per fill — meaningful over a year, trivial to capture.
Frequently asked questions
How much does gas cost for a 500-mile trip?
At 28 MPG and $3.40/gallon: about $61 (17.9 gallons). A 20 MPG SUV pays $85; a 38 MPG hybrid about $45.
How do I calculate gas cost per mile?
Gas price divided by MPG. $3.40 ÷ 28 = about 12 cents per mile of fuel. Total driving cost including wear runs 60–70 cents/mile.
How much should passengers chip in for gas?
Fuel cost divided by everyone including the driver is the friendly baseline. For long trips, adding a share of wear (IRS-style full rate) is fairer to the car owner — two to three times the fuel-only number.
Does driving slower really save gas?
Yes — aerodynamic drag grows with the square of speed. Dropping from 80 to 65 mph typically improves economy 15–25%, the cheapest fuel discount available.
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Last updated: 2026-07-08