Question: one gallon is how many litres of water?
Answer: 1 US fluid gallon is equal to 3.785411784 liters and 1 Imperial gallon is equal to 4.54609 liters. The symbol is "gal". The US fluid gallon is defined as 231 cubic inches (3.785411784 liters), the US dry gallon is defined as ​1⁄8 US bushel (4.4048838 liters) and the imperial gallon is defined as 4.54609 liters.