A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl. , old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume equal to ⁄20 of a pint or ⁄160 of a gallon in the imperial system or ⁄16 of a pint or ⁄128 of a gallon in the US system. The imperial gallon was originally defined as the volume occupied by 10 pounds avoirdupois of water at 62 degree Fahrenheit, but is currently defined as 4.54609 litres, making the imperial fluid ounce exactly 28.4130625 mL.