Fuel Economy Converter — MPG, L/100km & km/L
Convert fuel economy between US mpg, UK (imperial) mpg, L/100km and km/L — enter one and see all the others instantly, in your browser.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
US and UK (imperial) gallons differ, so their mpg figures are not the same. L/100 km is inverse — a lower number is more efficient. Click any value to copy.
About this tool
Cars sold in different countries quote their fuel economy in different units, which makes them awkward to compare. This converter switches a figure between US miles per gallon, UK (imperial) miles per gallon, litres per 100 km and kilometres per litre. Enter the unit you have and the others appear at once. Note that L/100km works the opposite way round to mpg — a lower number means better economy. It all runs in your browser, so your figures stay on your device.
Frequently asked questions
Why is US mpg different from UK mpg?
Because the two gallons are different sizes. A US gallon is about 3.785 litres, while a UK (imperial) gallon is about 4.546 litres — roughly 20% larger. Since a UK gallon holds more fuel, the same car covers more miles on it, so its UK mpg figure looks higher than its US mpg even though nothing about the car has changed.
What does L/100km mean, and why is a lower number better?
L/100km measures how many litres of fuel a car uses to travel 100 kilometres, the standard in much of Europe and Asia. It is an inverse measure: the less fuel needed for that distance, the lower the figure, so a smaller number means better economy. That is the opposite of mpg and km/L, where a higher number is better, which is easy to mix up when comparing cars.
Is my data sent anywhere?
No. All of the conversions run locally in your browser, so the fuel-economy figures you enter are never uploaded to or stored on a server. Nothing leaves your device, so you can compare cars privately, and once the page has loaded the tool keeps working even without a connection.