Fuel Economy Converter

Convert fuel economy between MPG, L/100km, and km/L

Enter a value, pick its unit, and this tool instantly shows the equivalent in all four common measures of fuel economy: miles per gallon (US), miles per gallon (UK / imperial), litres per 100 kilometres, and kilometres per litre. It is handy when comparing a car advertised in one region against figures you are used to elsewhere, or when reading a spec sheet that mixes units. Everything is computed in your browser as you type — nothing is uploaded.

The conversions use exact definitions: 1 US gallon = 3.785411784 litres, 1 UK gallon = 4.54609 litres, and 1 mile = 1.609344 kilometres. The US and UK gallons differ, so the same MPG figure means a different real-world efficiency depending on which gallon was intended — 30 MPG (US) is about 36 MPG (UK). Always check which gallon a quoted MPG refers to before comparing.

Why L/100km goes the other way

MPG and km/L are "distance per fuel" measures, so a bigger number is better. L/100km is the inverse — "fuel per distance" — so a smaller number is better. A frugal car might read 5 L/100km, while a thirsty one reads 12 L/100km. Keep that flip in mind: improving from 8 to 6 L/100km is a meaningful gain, even though the number went down.

FAQ

What is the difference between US and UK MPG? The imperial (UK) gallon is about 20% larger than the US gallon, so a UK MPG figure is always higher than the US figure for the same car. Convert between them before comparing vehicles sold in different markets.

How do I convert MPG to L/100km? Enter your MPG value, select MPG (US) or MPG (UK), and read the L/100km result. As a rough US check, 235.2 divided by MPG (US) gives L/100km — so 30 MPG ≈ 7.84 L/100km.

Is a lower L/100km better? Yes. L/100km measures fuel used per distance, so lower means the car uses less fuel and is more efficient. This is the opposite of MPG and km/L, where higher is better.

What is km/L? Kilometres per litre is a distance-per-fuel measure used in several countries. Higher is better, and 30 MPG (US) is roughly 12.75 km/L.