Convert gallons to liters

The formula

liters = gallons × 3.7854118

gallons to liters — quick reference

The American gallon is the smaller one, by a fifth

Read gallons as US gallons of 3.785 litres unless the source is British and old. The imperial gallon is 4.546 litres, and the two sit far enough apart that a mistaken reading is never a rounding matter. A US gallon of milk is 3.79 litres; the British supermarket equivalent is a four-pint bottle at 2.27 litres, which is half an imperial gallon and not a gallon of anything.

Context usually settles it. Anything measured in gallons in a modern British setting is either a car’s fuel economy or a survival from before 1995, when the imperial gallon stopped being legal for trade. Anything from an American recipe, hardware shop, pool supplier or aquarium listing is a US gallon, and the seller will never say so, because there is only one gallon where they are standing.

Container sizes are names, not measurements

A five-gallon bucket is nominally 18.9 litres and usually holds a litre or two more, because the nominal figure describes the working fill rather than the brim. Buying the metric substitute means buying a 20-litre pail, which is a different object with a different capacity, not a translation of the same one.

The pattern repeats at scale. The American 55-gallon drum is 208 litres; the European standard is a 200-litre drum. Anyone ordering, costing or dosing against a converted figure — pool chemicals, agricultural spray, anything measured per unit of volume — is working from a container four per cent smaller than the one the instructions assumed.

Questions