Gas Mileage Calculator
Calculate measured miles per US gallon from the distance driven and fuel used between refills.
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How to Use the Gas Mileage Calculator
Fill the tank and reset the trip meter. Drive normally, then refill to a comparable level. Enter the miles traveled and the US gallons added at the second fill, then calculate. Use a longer representative interval to reduce the effect of small refill differences.
Formula and Explanation
MPG = Miles driven ÷ US gallons used
Dividing miles driven by gallons used gives miles per gallon. The fuel added at the second full-tank refill approximates the fuel consumed since the first fill, provided both fills reached a similar level.
This measures an average over the entered interval. Partial fills, different filling levels or an inaccurate trip reading can distort the result. The tool accepts miles and US gallons only; imperial gallons and liters are not interchangeable with US gallons.
Worked Example
If you drive 312.5 miles and add 12.5 US gallons to refill the tank, your measured fuel economy is 312.5 ÷ 12.5 = 25 MPG. Use that measured value in the Fuel Cost Calculator when budgeting a similar trip.
Frequently Asked Questions
Should I enter tank capacity or the fuel I bought?
Enter fuel actually used over the measured distance. With the full-tank method, this is approximated by the amount needed at the second refill, not your vehicle’s nominal tank capacity.
Does MPG use US or imperial gallons?
This calculator uses US gallons. An imperial gallon has a different volume, so an imperial MPG figure cannot be compared directly without conversion.
Can I average several tanks?
Yes. Add the miles across comparable refill intervals and divide by the total US gallons used. Do not simply average each tank’s MPG when the amounts of fuel differ.
Why does my result differ from the dashboard?
Dashboard estimates and refill measurements use different inputs and may cover different intervals. Filling level, trip-meter readings and driving conditions can also affect the comparison.