Convert gallon (imperial) to milliliter

Recipes give ingredients either by volume (millilitres, cups, spoons) or by weight (grams, ounces), and the two cannot be converted directly: the weight of a given volume depends on the ingredient. A cup of water weighs about 240 g, a cup of flour only about 125 g and a cup of sugar about 200 g. The link between the two is the density of the ingredient.

The UK and the US kept different gallons after 1824. The imperial gallon is 4.546 l and the US gallon 3.785 l, so a US gallon is only five-sixths of a British one; the same applies to their quarts and pints, and a British pint of beer (568 ml, 20 fl oz) is bigger than an American one (473 ml, 16 fl oz). The US also has a separate dry gallon of 4.405 l for grain and produce. Fuel is sold by the litre in Britain today but by the US gallon in America, which matters for fuel-economy figures.