Fuel Economy Converter
Convert fuel economy between miles per gallon, liters per 100 km, kilometers per liter, and miles per liter, with the US and imperial gallons kept apart. These units run in opposite directions: a higher MPG is better, a higher L/100km is worse, so the conversion is a division rather than a multiplication.
Converters
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How it works
Why the two scales run in opposite directions
L/100km = 235.2146 ÷ MPG (US) · L/100km = 282.4809 ÷ MPG (imperial)
Miles per gallon counts distance travelled per unit of fuel; liters per 100 km counts fuel used per unit of distance. One is the reciprocal of the other, so the conversion divides a constant by your figure instead of scaling it.
- The constants come straight from the unit definitions: 3.785411784 L per US gallon and 1.609344 km per mile, scaled to 100 km.
- Because the scales are reciprocal, equal MPG steps are not equal savings. Going from 10 to 15 MPG saves more fuel over the same distance than going from 30 to 60 MPG.
- Canada and most of Europe quote L/100km; the UK quotes imperial MPG; the US quotes US MPG. Comparing brochures across markets needs the gallon checked first.
- Electric vehicles use kWh/100km or MPGe, which are not covered here — those measure energy, not liquid fuel.
For reference
US MPG against liters per 100 km
| MPG (US) | L/100km | km/L | MPG (imperial) |
|---|---|---|---|
| 15 | 15.68 | 6.38 | 18.01 |
| 20 | 11.76 | 8.50 | 24.02 |
| 25 | 9.41 | 10.63 | 30.02 |
| 30 | 7.84 | 12.75 | 36.03 |
| 40 | 5.88 | 17.01 | 48.04 |
| 50 | 4.70 | 21.26 | 60.05 |
Notice the L/100km column closing up as MPG rises: the same 10 MPG improvement is worth far less at the top of the table than at the bottom.
How to use
4 clear steps.
Enter the fuel economy figure from the brochure or trip computer.
Select its unit, choosing US or imperial MPG deliberately.
Select the unit you want and read the converted figure.
Compare all units at once in the full table.
Good to know
Frequently asked questions
- How do I convert MPG to L/100km?
- Divide 235.215 by the US MPG figure. 30 MPG is 235.215 ÷ 30 = 7.84 L/100km. For imperial MPG, divide 282.481 instead.
- Why are UK MPG figures higher than US ones?
- The imperial gallon is 4.546 L against the US gallon's 3.785 L, so the same car travels further on one imperial gallon. A car rated 30 MPG in the US is about 36 MPG in the UK — identical fuel use, different gallon.
- Why is the conversion a division and not a factor?
- MPG measures distance per fuel and L/100km measures fuel per distance, so they are reciprocals. That is also why the difference between 10 and 15 MPG matters far more than between 40 and 45 MPG.