Gas mileage calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- mpg = miles ÷ gallons = 350 ÷ 12.5 = 28.
- L/100 km = 235.214583 ÷ mpg (1 US gallon = 3.785411784 L, 1 mile = 1.609344 km).
| Inputs | Answer |
|---|---|
| Distance: 350; Fuel used: 12.5 | 350 miles on 12.5 gallons is 28 miles per gallon (8.4 L/100 km). |
| Distance: 420; Fuel used: 11 | 420 miles on 11 gallons is 38.18 miles per gallon (6.16 L/100 km). |
| Distance: 180; Fuel used: 9 | 180 miles on 9 gallons is 20 miles per gallon (11.76 L/100 km). |
How to use it
Fuel economy in miles per gallon is distance ÷ fuel. 350 miles on 12.5 gallons is 28 mpg. The calculator converts it to litres per 100 km (235.214583 ÷ mpg), the unit used in much of the world, and kilometres per litre.
For the most accurate figure, fill the tank, drive, then fill again and use the gallons it takes.
Frequently asked questions
How do I calculate mpg?
Divide the miles driven by the gallons of fuel used.
How do I convert mpg to L/100 km?
Divide 235.214583 by the mpg.
Are US and UK gallons the same?
No; a UK (imperial) gallon is 4.54609 litres and a US gallon 3.785411784 litres.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.