The gallon is a unit of volume in the imperial unit system with the symbol gal.
1 British imperial gallon is defined as 4.54609 litres or 277.4194 in³.
The term gallon derives directly from the Old Northern French term 'galun' which means 'liquid measure'. The origin of the word prior to this is still unknown. It originated as the base of the system for measuring wine and beer in the UK and has now been adopted across the world and there are similar versions in the US and associated states (although they measure slightly differently).
The imperial fluid ounce is a unit of volume from the imperial unit system and uses the symbol fl oz.
1 imperial fluid ounce is equal to 28.41306 ml. It is also equivalent to 0.9607599 US fl oz.
The imperial gallon was defined in Britain by Parliament in 1824 and established as ten pounds of water at a normal temperature. This was split into 4 quarts, each quart into 2 pints, each pint into 4 gills and each gill into 5 ounces.
Therefore; 1 imperial fluid ounce is equal to 1/20 imperial pint, 1/40 imperial quart and 1/160 imperial gallon.