Gas Mileage Calculator
Work out your car’s real MPG from miles driven and gallons filled — plus what each mile costs you.
How it works
MPG = miles driven ÷ gallons refilled · cost per mile = price ÷ MPG
The fill-up method: top the tank until the pump clicks off, reset the trip odometer, drive normally, then refill to the click. The gallons the second fill takes are exactly what those miles consumed, so miles ÷ gallons is your true MPG. One tank has some noise in it — average three or four tanks for a solid number.
Worked example
320 miles on an 11.5-gallon refill is 320 ÷ 11.5 = 27.8 MPG. At $3.50 per gallon that works out to 12.6¢ per mile, or $12.58 per 100 miles.
Frequently asked questions
Why is my MPG lower than the EPA sticker?
Stickers come from standardized lab cycles. Short trips with cold engines, winter fuel blends, AC use and stop-and-go traffic commonly cost 10–20% versus the rating.
Why does one tank read oddly high or low?
Pump shutoff points vary and parking on a slope changes how much fits, so single-tank numbers wobble. The average across several tanks is the honest figure.
Does premium gas improve MPG?
Only in engines that require or specifically tune for it. In a regular-fuel engine, premium mostly buys nothing — check the owner’s manual, not the pump label.
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This calculator is for educational purposes. Double-check important results before acting on them.