Fuel economy converter (mpg, L/100 km, km/L)
Miles per gallon (US and UK), litres per 100 km and kilometres per litre, converted with the correct reciprocal formulas.
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Fuel economy is quoted two ways. Distance per fuel (miles per gallon in the US and UK, kilometres per litre in India, Japan and much of Latin America) grows as a car gets more efficient. Fuel per distance (litres per 100 km, used in Europe, Australia, China and the Gulf) shrinks. Converting between them is a reciprocal, not a multiplication, which is why the formula line shows a division.
The constants follow from the exact mile (1.609344 km) and gallons: L/100 km = 235.2146 ÷ mpg (US) and L/100 km = 282.4809 ÷ mpg (UK); km/L = 100 ÷ L/100 km. A car rated 30 mpg in the US uses 7.84 L/100 km; the same car is about 36 mpg in UK units, because the imperial gallon is 20% larger. Zero cannot be inverted, so 0 L/100 km or 0 mpg shows a dash instead of infinity.
Because of the reciprocal, improvements look different on each scale: going from 10 to 20 mpg saves far more fuel than going from 40 to 50 mpg, which is obvious in L/100 km (23.5 → 11.8 versus 5.9 → 4.7).
How to use it
- Pick the figure you have: US mpg, UK mpg, L/100 km or km/L.
- Pick the scale you want and type the value in either box.
- Check the table for common ratings.
Frequently asked questions
How do I convert mpg to L/100 km?
Divide 235.215 by US mpg (or 282.481 by UK mpg). 25 mpg (US) = 9.41 L/100 km.
Why is UK mpg higher than US mpg for the same car?
An imperial gallon is 4.546 L and a US gallon 3.785 L, so a car travels about 20% farther on a UK gallon. Multiply US mpg by 1.201 to get UK mpg.
How do I convert km/L to L/100 km?
Divide 100 by the km/L figure. 15 km/L = 6.67 L/100 km.
What happens if I enter 0?
Zero has no reciprocal (it would mean infinite fuel economy or consumption), so the converter shows a dash and a note instead of a meaningless number.
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