Fuel Economy Converter
Turn any fuel-economy figure into a different unit — L/100km, MPG, or km/L — handling the inverse relationship correctly.
Inverse-aware
Consumption and efficiency are reciprocals, so the converter pivots through litres per 100 km rather than scaling by a single ratio.
US vs UK gallon
A US gallon is smaller than a UK gallon, so the same car shows a higher MPG in the UK. Pick the right gallon for an accurate result.
What is a fuel economy converter?
One figure, any unit
A fuel economy converter changes how efficiently a vehicle uses fuel from one unit into another — litres per 100 km to miles per gallon, MPG to kilometres per litre, and back. Different countries report fuel economy in different ways: Europe uses L/100km (how much fuel it takes to drive a fixed distance), the United States and United Kingdom use miles per gallon (how far you go on a fixed amount of fuel), and many other places use km/L. This tool covers all four so you can compare a car listed in one system against your own.
Fuel economy units are not a simple scale of one another. L/100km measures consumption, where a lower number is better, while MPG and km/L measure efficiency, where a higher number is better. Because one is the reciprocal of the other, the converter pivots through a single base — litres per 100 km — and inverts on the way in and out.
L/100km = 235.21 ÷ MPG (US)The relationship is inverse: 8 L/100km converts to 29.4 MPG, but 4 L/100km — half the consumption — converts to about 58.8 MPG, double the efficiency. A smaller L/100km figure and a larger MPG figure both describe a more economical car. The constant 235.21 comes from combining the size of a US gallon (3.785 litres) with the length of a mile (1.609 km); the UK gallon is larger, so its constant is 282.48 instead.
Suppose a European car is rated at 8 L/100km and you want to know its US MPG.
Start from the base
The car already uses L/100km — the converter's base unit — so the figure is 8.Divide the constant by the figure
US MPG uses the constant 235.21, so 235.21 ÷ 8 = 29.4.Read the result
8 L/100km converts to about 29.4018 MPG (US) — a higher number for the same, better economy.
Read the direction of the units before comparing. With L/100km, lower is better — 5 L/100km is more economical than 8. With MPG and km/L, higher is better — 50 MPG beats 30. The two MPG figures are not interchangeable: a US gallon (3.785 L) is smaller than a UK gallon (4.546 L), so the same car always shows a higher MPG when measured in UK gallons. If you are comparing a US window sticker against a UK advert, convert both to the same unit first, or you will overstate the difference by about 20%.
The arithmetic is exact; real-world driving is not.
Rated versus real-world economy
Manufacturer and regulator figures come from standardised test cycles, so your actual economy will vary with driving style, traffic, load, weather, and fuel grade. The converter changes units exactly, but it cannot make a rated MPG match what you see at the pump. Because the units are reciprocals, never convert a value of zero — a fuel economy of zero has no finite counterpart — and remember that a small change in L/100km maps to a larger change in MPG at high efficiency.