Formula
- Gallons needed = miles ÷ mpg
- Trip cost = gallons × price per gallon
- Cost per mile = price per gallon ÷ mpg
A 280-mile trip in a car that gets 28 mpg with gas at $3.25 a gallon uses 10 gallons and costs $32.50 one way, or $0.116 per mile.
How to measure your real mpg
- Fill the tank and reset the trip meter.
- Drive normally, then fill up again.
- Divide the miles driven by the gallons it took to refill.
This is usually more accurate than the dashboard estimate. Use “Work out your real mpg” above.
What is not included
Tolls, parking, wear and tear and depreciation are not part of fuel cost. Highway speed, A/C, roof boxes and heavy loads can cut mpg noticeably.