MPG Calculator
Work out your fuel economy from the distance driven and fuel used, shown as mpg, L/100km, and km/L, with the cost per mile and per km. Handles imperial and metric. Calculates in your browser.
Fuel economy
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Show the math
Economy is distance over fuel; the two systems are reciprocals:
mpg = miles ÷ gallons
L/100km = litres ÷ km × 100
mpg × (L/100km) = 235.21
US gallons are assumed (a UK gallon is larger). The conversion constant 235.21 links US mpg and L/100km exactly. All math runs locally in your browser.
What this does
An MPG calculator works out your fuel economy from the distance driven and fuel used, shown as mpg, L/100km, and km/L, with the cost per mile and per km.
How it works
Divide the miles driven by the gallons used between fill-ups. For an accurate figure, fill the tank, reset the trip meter, then divide the trip distance by the gallons it takes to refill.
MPG = miles ÷ gallons
How to use it
- Enter the distance driven.
- Enter the fuel used.
- Choose your units.
- Read your fuel economy and cost per mile.
Understanding your result
MPG and L/100km are reciprocals linked by a constant: US mpg × L/100km = 235.21. This tool uses US gallons; a UK gallon is about 20% larger.
Example
300 miles on 10 US gallons is 30 mpg, about 7.84 L/100km.
Sources & methodology
- U.S. DOE/EPA, fueleconomy.gov, Official fuel economy ratings
Last updated .
Frequently asked questions
How do I calculate MPG?
Divide the miles driven by the gallons used between fill-ups. For an accurate figure, fill the tank, reset the trip meter, then divide the trip distance by the gallons it takes to fill up again.
How does mpg relate to L/100km?
They are reciprocals linked by a constant: US mpg × L/100km = 235.21. So 30 mpg is about 7.84 L/100km.
Are these US or UK gallons?
US gallons. A UK (imperial) gallon is about 20% larger, so UK mpg figures look higher for the same real economy.
Is my data saved?
No. All calculations happen locally in your browser.
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