Convert gallon (u.s. liquid) to gallon (imperial)

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.