Convert Miles per Gallon (US) to Liters per 100km

Two Systems, Opposite Logic

MPG and L/100km use opposite fuel-economy logic. MPG asks "how far can I go on one gallon?" (bigger is better). L/100km asks "how much fuel do I burn over 100 kilometers?" (smaller is better). That inversion changes how you should think about fuel savings.

The quick conversion formula: divide 235 by the MPG value to get approximate L/100km. So 30 MPG is roughly 235/30 = 7.8 L/100km. Going the other direction, divide 235 by L/100km to get MPG.

The MPG Illusion

This is the most important thing this converter page can teach you, and it is something the numbers alone do not reveal.

Improving from 15 to 20 MPG saves more fuel than improving from 30 to 40 MPG, even though "10 MPG improvement" sounds bigger than "5 MPG improvement." This is counterintuitive until you see it in L/100km, where the math becomes linear and honest:

• 15 to 20 MPG: 15.7 to 11.8 L/100km = saves 3.9 liters per 100 km
• 30 to 40 MPG: 7.8 to 5.9 L/100km = saves 1.9 liters per 100 km

The first upgrade saves twice as much fuel. This is because MPG has a hyperbolic relationship with fuel consumption. Small improvements at the low end of the MPG scale deliver outsized savings, while big jumps at the high end barely matter. Researchers at Duke University called this the "MPG Illusion" in a 2008 paper, and it has real consequences for policy. Replacing a 15 MPG truck with a 20 MPG truck does more for total fuel consumption than replacing a 30 MPG car with a 50 MPG hybrid.

L/100km avoids this illusion entirely because it measures consumption directly. This is one reason most of the world uses it.

The UK vs US Gallon Trap

If you are converting between American and British fuel economy figures, beware: a UK gallon (imperial gallon) is about 20% larger than a US gallon.

• 1 US gallon = 3.785 liters
• 1 UK gallon = 4.546 liters

This means a car rated at 40 MPG in the UK gets only about 33 MPG by US standards, even though it is the exact same car burning the exact same amount of fuel. British fuel economy figures always look better because the gallon is bigger. Our converter uses US gallons (the global default for MPG). If you need UK MPG, use the "Mile per Gallon (UK)" unit in the fuel economy category instead.

Why This Matters for Car Shopping

When comparing vehicles across markets, L/100km is the only reliable common ground. A European review saying "5.2 L/100km" and an American review saying "45 MPG" describe nearly the same car. Without converting, those numbers look unrelated.

For more on fuel economy ratings and why your real-world mileage rarely matches the sticker, see our fuel economy ratings explained article.