Fuel Economy Converter

Fuel economy quantifies how efficiently a vehicle uses fuel over distance. The metric system expresses it as volume consumed per distance (L/100 km), a direct measure of fuel consumption. The US and UK use the inverse form: distance per volume (miles per gallon, mpg). Because the US and imperial gallon differ by 20% (3.785 L vs 4.546 L), US mpg and imperial mpg ratings are not interchangeable for the same vehicle. The kilometre per litre (km/L) used in Japan is the mathematical reciprocal of L/100 km, scaled by 100.

All conversions in this category are computed relative to a single base unit (Liters per 100 km) using factors sourced from NIST Special Publication 811 and the BIPM SI Brochure. A shared reference unit keeps the conversion relationships consistent. Converting directly from the original measurement avoids the rounding differences that can accumulate when displayed intermediate results are entered again.

This calculator supports 6 units, including Liters per 100 km, Miles per Gallon (US), Miles per Gallon (Imperial), Kilometers per Liter, Liters per 100 miles. Choose the unit shown in your source measurement, then the unit needed for your result.

Units may have alternate spellings or abbreviations. You can search using these names too. Examples include Liters per 100 km (L100km, also written as L/100km or l/100km), or Miles per Gallon (US) (mpg-us, also written as mpg or mpg US), or Miles per Gallon (Imperial) (mpg-imp, also written as mpg imp or imperial mpg).

Depending on the fuel economy pair, conversion may use a scale factor, an offset, or a reciprocal formula. Each converter page shows the formula for that pair, along with a worked example and a reference table.

Results and displayed coefficients are rounded for readability, usually to ten significant digits; very large or small results use scientific notation. Work from the original measurement and apply the rounding appropriate to its accuracy. A manual calculation using a displayed coefficient can differ slightly from the converter result.

Keep the unit alongside each fuel economy value when you copy or share it. Check that the source and target units match your task. If two units have similar names, read their definitions before selecting one.

For a second check, use the worked example and formula on the conversion page. Start from your original value rather than a rounded result from another calculator. If you need to report a specific number of decimal places, round once at the end.