Understanding your result
Lower L/100 km means less fuel per distance. Higher km/L or mpg means more distance per fuel volume. The distance table applies the converted consumption rate unchanged to illustrative journeys.
If the journey distance is in another unit, convert it with the Length Converter .
The formula
The constants follow from 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, and 1 Imperial gallon = 4.54609 L. Consumption and economy are reciprocals, so this is not a simple multiplication by one fixed factor across all modes.
Worked example
A vehicle using 8 L/100 km travels 12.5 km per litre. This is approximately 29.4018 US mpg or 35.3101 Imperial mpg. At the same rate, a 500 km journey would consume 40 litres.
How to use this calculator
- Copy the fuel figure from a vehicle specification or measured trip.
- Choose its exact unit, including the gallon standard where applicable.
- Compare converted figures on the same unit and test basis.
A gallon difference can look like an efficiency difference
The Imperial gallon is larger than the US liquid gallon. The same vehicle therefore records a higher numerical mpg value when Imperial gallons are used. A specification that says only mpg is incomplete for an international comparison. Check the market and source documentation before deciding which input unit to choose.
Conversion does not equal a road-test prediction
Driving conditions, speed, load, weather, and the test cycle influence actual consumption. This tool converts units only; it does not reconcile different testing procedures or predict a particular trip. To combine multiple trips, total their fuel and distance before calculating economy. An unweighted average of mpg values can produce the wrong combined result when trips differ.
Assumptions & limitations
What this calculation assumes
- Fuel volume and distance refer to a consistent measurement or stated rating.
What to keep in mind
- Positive values only; no electric MPGe, fuel-price forecast, or test-cycle adjustment.
Common questions
Why is zero rejected?
The reciprocal conversions would be undefined. Zero fuel consumption is not a finite miles-per-gallon value.
Can I compare diesel and petrol figures?
You can compare volume-based units, but this does not equalize fuel energy content, emissions, or cost per litre.