How to calculate gas cost for a trip
Divide trip miles by your vehicle’s MPG to find gallons needed. Multiply gallons by the current price per gallon. A 500-mile trip at 28 MPG uses about 17.86 gallons; at $3.50 per gallon it costs about $62.50.
Gallons = trip miles ÷ MPG
Fuel cost = gallons × price per gallon
Fuel cost per mile and per year
Cost per mile is gas price divided by MPG. It makes vehicles with different fuel economy easy to compare. Annual fuel cost multiplies that rate by expected yearly mileage; maintenance, insurance and depreciation are not included.
EPA MPG vs. real gas mileage
Published fuel economy is a useful baseline, but speed, weather, traffic, towing and tire pressure change real consumption. For a personal estimate, calculate MPG across several full-tank fill-ups and use the average.