Fuel economy converter
Convert fuel economy between L/100 km, km/L and miles per gallon.
Fill in the fields and the result will appear here automatically.
Converts L/100 km, km/L and US or UK mpg. Consumption per distance and distance per fuel are inversely related: doubling L/100 km halves mpg. The relationship between km/L and mpg is proportional. The gallons differ, so their mpg values are shown separately.
How it works
Formula and logic
Every unit is routed through L/100 km. Kilometres per litre are inversely related: 100 ÷ value. Miles per gallon convert as 100 × gallon volume ÷ (value × 1.609344). A US gallon is 3.785411784 L and an imperial gallon 4.54609 L.
Example
A consumption of 8 L/100 km is 12.5 km/L, 29.402 mpg (US) and 35.31 mpg (UK).
Fields and units
- Value — in the selected source unit
- From unit — list option
- To unit — list option
How to use
- — Enter the consumption figure.
- — Choose the unit it is given in.
- — Choose the unit you want.
- — The other three are shown alongside for comparison.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- NIST: international mile, US and imperial gallons — unit conventions used for mpg
- Limitation
- Converts units for the entered value. It does not predict actual consumption or payback; displayed numbers are rounded.
FAQ
Why can't I just multiply by a factor?
Because the relationship is inverse rather than proportional. Litres per hundred kilometres rise as miles per gallon fall, so the conversion goes through a division and no constant multiplier between them exists.
How do US and UK mpg differ?
For the same actual consumption, UK mpg is about 20.1% higher numerically than US mpg because the gallon is larger. The same number, such as 30 mpg, describes different consumption in the two systems; select the stated gallon.
Which unit is used where?
Litres per 100 km are standard in continental Europe, kilometres per litre in parts of Asia and Latin America, and miles per gallon in the US and the UK.
Is a lower number better or worse?
It depends on the unit, and that is the usual source of confusion. For litres per 100 km lower is better; for kilometres per litre and miles per gallon higher is better.
Does the same saving in L/100 km save the same amount of fuel?
Yes, over the same distance. Both 10→9 and 6→5 L/100 km save 1 L per 100 km, or 10 L over 1000 km. The corresponding changes in mpg differ because the relationship is inverse; payback also needs cost and distance information.