Fuel Economy Converter
Convert between mpg and L/100km — both directions.
The Fuel Economy Converter translates between the two ways the world rates fuel use: miles per gallon (US and the mpg-loving public) and liters per 100 kilometers (the metric standard). Enter either figure and read the other instantly.
The relationship is inverse, which confuses newcomers: higher mpg and lower L/100km both mean better economy — 30 mpg is about 7.8 L/100km, and a car doing 5 L/100km is doing about 47 mpg. Comparing across systems without converting produces exactly the kind of error this tool removes.
Note the units matter: this converter uses US gallons (3.785 L). UK gallons are 20% larger, so imperial mpg figures are higher for the same car. Runs locally in your browser.
US mpg
30.00
L/100 km
7.84
km per liter
12.75
Conversion formulas: L/100km = 235.215 ÷ mpg, km/L = mpg × 0.425. Note UK gallons differ (1 imperial gallon = 4.546 L) — this tool uses US gallons. Lower L/100km and higher mpg both mean better economy.
How to use the Fuel Economy Converter
- Enter a fuel economy value.
- Choose its unit: US mpg or L/100km.
- Read the converted figure.
- Check the km/L reading too.
- Use it when comparing imported spec sheets or reviews.
Frequently asked questions
How do I convert mpg to L/100km?
L/100km = 235.215 ÷ mpg. So 30 mpg = 7.84 L/100km and 40 mpg = 5.88 L/100km. The constant comes from converting gallons to liters and miles to 100 km.
Is US mpg different from UK mpg?
Yes — the imperial gallon is 4.546 L versus 3.785 L for the US gallon. The same car rates about 20% higher in imperial mpg. This tool uses US gallons; convert with the UK factor (282.5 ÷ imperial mpg) if needed.
Which unit should I use?
Match your market: US reviews quote mpg, Europe and most of the world quote L/100km. For international comparisons, L/100km is the more honest unit because it scales linearly with fuel cost.
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