A quart is a quarter gallon — but which gallon?
The US liquid quart is a quarter of the 3.785-litre US gallon, exactly 0.946352946 L. The imperial quart is a quarter of the 4.546-litre imperial gallon, 1.1365 L, a full 20% larger. Motor oil, ice cream and milk in the US are sold by the US quart; the imperial quart is now rare even in Britain, where litres and pints took over. There is also a US dry quart of 1.101 L used for produce, which the calculator does not use.
litres = quarts (US) × 0.946352946 | quarts (US) = litres ÷ 0.946352946
Rough conversion in your head
A US quart is a litre minus 5%, so quarts and litres are nearly interchangeable for cooking: 2 qt of stock is 1.9 L. Four quarts is a gallon, 3.79 L. Going from litres, add 5%: a 2 L bottle is 2.11 US quarts, or just over half a gallon.