A
fluid ounce (abbreviated
fl oz,
fl. oz. or
oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of
volume (also called capacity) typically used for measuring liquids. It is equivalent to approximately 30
millilitres. Whilst various definitions have been used throughout history, two remain in common use: the
imperial and the
United States customary fluid ounce. An imperial fluid ounce is of an imperial
pint, of an imperial
gallon or approximately 28.4 ml. A US fluid ounce is of a
US fluid pint, of a US liquid gallon or approximately 29.6 ml. The fluid ounce is distinct from the
ounce, a unit of
weight or
mass, although they do have a historical relationship, and it is sometimes referred to simply as an "ounce" where context makes the meaning clear.