imp fl oz
imperial fluid ounce
Volumeexact by definition
The imperial fluid ounce is exactly 1/160 of an imperial gallon, 28.4130625 millilitres. It is used in the United Kingdom, Ireland and much of the Commonwealth, and it is about 4% smaller than the US fluid ounce.
Watch out: The US fluid ounce is 29.5735 mL. The imperial ounce is smaller but the imperial pint is larger, because a US pint holds 16 fluid ounces and an imperial pint holds 20. Both differences run in opposite directions, which makes casual conversion between the systems unusually easy to get wrong.
| 1 imp fl oz | 0.028413063 L |
Where the unit came from
It was defined so that one imperial fluid ounce of water weighs almost exactly one avoirdupois ounce, which is why the imperial system's volume and mass units line up for water and the US system's do not.
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