The US fluid ounce is a unit of volume in the US customary unit system with the symbol fl oz.
Primarily used for measuring the volume or capacity of liquids, 1 US fluid ounce is equal to 29.57353 ml. It is also equal to 1.040843 imperial fluid ounces.
1 US fluid ounce is equal to 1/16 imperial pint, 1/32 imperial quart and 1/128 imperial gallon.
The fluid ounce was originally defined by the volume taken up by one ounce of a substance. Of course this would be different depending on the density of that substance; for example England used wine whereas Scotland used water to establish this measure.
The US fluid ounce is derived from the US gallon; which was originally based on the English wine gallon (231 cubic inches).
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.