Car / Fill-ups
Gas Mileage Calculator: Average MPG from Fill-Ups
Measure fuel economy from distance or odometer readings and fuel added. Combine fill-ups and optionally include prices for fuel cost per mile or kilometre.
Gas Mileage Calculator: Average MPG from Fill-Ups: Divides total distance by total fuel, which gives the correct combined economy even when refill amounts differ. Price entries produce a total fuel cost divided by total distance. The input gallon is the US gallon; UK MPG is also shown. Runs 100% locally in your browser with zero server file uploads.
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Changing currency does not convert prices. Unit changes preserve the same physical quantities.
Start with a full tank. For each following full refill, enter the distance since the previous full tank and the fuel added. Combine partial fills into one full-to-full interval.
The average is total distance divided by total fuel, not the arithmetic mean of the MPG figures. UK MPG uses the imperial gallon; fuel inputs use US gallons or litres.
Distance and fuel
US MPG = miles ÷ US gallons. UK MPG = miles ÷ imperial gallons. L/100 km = litres ÷ kilometres × 100. One international mile is exactly 1.609344 km; gallon definitions are listed in NIST SP 811, Appendix B: https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors
Combining records
Add distances and fuel volumes before dividing. Cost per distance uses the sum of each refill's fuel × price. Consistent full-to-full measurements reduce tank-level error; short intervals and inconsistent pump cut-off can distort results.
How to use it
- Start from a full tank and enter the distance to your next full refill, or its odometer readings.
- Enter fuel added and optionally its price; add more full-to-full intervals.
- Read fuel-weighted US MPG, UK MPG, L/100 km and optional cost per distance.
Privacy & limitations
Fill-up records remain in the page and are not uploaded or saved after you leave.
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Frequently asked questions
Why not average the individual MPG figures?
Refills can contain different amounts of fuel. Use total miles divided by total gallons; an arithmetic average of MPG can misstate the result.
Can I use partial refills?
Combine partial refills and their distances into a single interval that starts and ends with a full tank. Fuel added over that interval then approximates fuel consumed.
Which gallon does it use?
US fuel inputs use 3.785411784 litres per gallon. UK MPG uses 4.54609 litres per imperial gallon. Metric inputs use litres and kilometres.
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