Fuel Economy Converter

The Fuel Economy Converter is a free online tool that convert between mpg (us), mpg (uk), km/l, l/100km, and km/gallon fuel economy units. It runs entirely in your browser with no installation or sign-up needed.

US uses 3.785L gallon, UK uses 4.546L gallon. Same vehicle shows higher MPG in UK gallons.

L/100km is an inverse measure — lower is better. The converter handles this correctly.

Yes — client-side, no registration.

Absolutely. The Fuel Economy Converter processes everything client-side in your browser. No data is uploaded to or stored on any server. Your content remains private on your device at all times.

Yes, the Fuel Economy Converter is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.

No account or registration is needed. Simply open the Fuel Economy Converter in your browser and start using it immediately. There are no sign-up walls or usage restrictions.

Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.

The Fuel Economy Converter works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.

L/100km and MPG run in opposite directions, so you cannot just multiply — you have to invert. Divide 100 by the L/100km figure to get kilometers per liter, then convert that to miles per gallon using the correct gallon size. With the US gallon (3.785 L), 8 L/100km works out to roughly 29.4 MPG (US), and 6 L/100km to about 39.2 MPG (US); UK MPG figures come out around 20% higher because the Imperial gallon is larger. Doing this by hand is error-prone because of the inverse step and the two gallon sizes. This converter handles both automatically — enter your L/100km value, pick L/100km as the From unit, and it shows the matching US and UK MPG instantly, plus every other unit in the All Equivalents panel.

It comes down to what each unit measures. MPG and km/L are distance-per-volume units: they tell you how far you travel on a fixed amount of fuel, so more distance — a higher number — means better economy. L/100km flips the fraction around: it measures the volume of fuel burned to cover a fixed distance of 100 kilometers, so burning less fuel — a lower number — means better economy. That is why a thrifty European car might read 5 L/100km while a thirsty SUV reads 12 L/100km, even though higher would be better in MPG. This inverse relationship is the most common source of confusion when comparing cars across regions. The converter handles the math correctly in both directions, so a low L/100km value maps to the high MPG it actually represents — try entering a figure to see all equivalents at once.

Using the US gallon, 5 L/100km is about 47 MPG (US), 6 L/100km is about 39.2 MPG (US), and 8 L/100km is roughly 29.4 MPG (US) — small drops in L/100km translate into meaningful MPG gains because the relationship is inverse, not linear. In UK (Imperial) MPG the same figures read noticeably higher, since the Imperial gallon holds about 4.546 liters versus the US gallon's 3.785 liters. These are the kinds of numbers you meet reading a European brochure quoted in L/100km and wanting a US frame of reference. Rather than memorize a table, enter the L/100km value into this converter: it returns both US and UK MPG along with km/L and km/gallon, and the built-in reference table maps common figures like 30, 40, and 50 MPG to every unit for quick sanity checks.

Because a "gallon" is not a single fixed volume. The US gallon holds about 3.785 liters, while the UK (Imperial) gallon holds about 4.546 liters — roughly 20% larger. Since MPG is miles traveled per gallon, a bigger gallon means more miles per gallon for the exact same fuel efficiency. So an identical car rated 40 MPG in the UK is only about 33 MPG (US), and the two figures differ by that same ~20% factor every time. This is why British and American reviews of one model can quote very different numbers without either being wrong. The converter keeps US and UK MPG as strictly separate units so you never accidentally compare across the wrong gallon — select the right MPG variant as your From unit and read the equivalent in the other directly.

Yes — the conversions here use exact physical constants rather than rounded shortcuts, so the results are precise to the figures you enter. Internally every value is first normalized to kilometers per liter and then expressed in your target unit, using 1 mile = 1.609344 km, the US gallon = 3.785411784 L, and the UK gallon = 4.54609 L. L/100km is treated as a true inverse (100 divided by km/L) so the better-is-lower logic stays correct in both directions, and km/gallon variants multiply by the matching gallon size. The only thing to keep in mind is that the input itself must be accurate, since converting a manufacturer's optimistic rating won't make it match real-world driving. Enter your value and the converter shows all six equivalents at once, with the formula displayed so you can verify the relationship.