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.
The acre-foot is a unit of volume in the US customary unit system with the symbol ac⋅ft.
It represents the volume contained in a box measuring 660 feet long, 66 feet wide and 1 foot deep. This can be thought of a box the size of an acre but 1 foot deep.
It is approximately the same volume as an 8 lane swimming pool; 25 metres in length, 3 metres deep and 16 metres wide (assuming lanes are 2 metres wide).
It is still used in the US despite its links to the much-outdated imperial system of units. For example a "rule of thumb" is that an average suburban family's annual water usage should be around 1 acre-foot. This is equal to just under 3.4 m³ daily.