Litres to Gallons

US gallon vs UK gallon — they are not the same

This is the most important thing to know when converting litres to gallons: a US gallon (3.785 litres) and a UK imperial gallon (4.546 litres) are completely different sizes. The UK gallon is about 20% larger. This means a car described as getting 40 mpg in the UK would be rated at roughly 33 mpg in the US — same car, same fuel economy, different mpg figures because the gallon is a different size.

Fuel economy is the most common place this conversion matters. European cars are rated in litres per 100 kilometres (L/100km). American cars use miles per gallon (mpg, US gallon). UK cars use mpg but with the imperial gallon. A car doing 6 L/100km converts to about 39 UK mpg or 47 US mpg. These are not interchangeable — quoting the wrong one will significantly mislead.

Drinking water and bulk liquid containers are often sized in gallons in the US. A standard water cooler bottle is 5 US gallons (18.93 litres). A US milk jug is 1 gallon (3.785 litres). Swimming pool capacity is often quoted in gallons in the US and litres in Europe. A backyard pool of 50,000 litres is approximately 13,200 US gallons or 11,000 UK gallons.

For recipe conversion, remember that American recipes use US gallons and cups (based on the US gallon), while British recipes may use imperial fluid ounces and pints (based on the UK gallon). The safest approach is to convert everything to millilitres for precision.