Fluid Ounce

A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume equal to 1⁄₂₀ of a pint or 1⁄₁₆₀ of a gallon in the imperial system or 1⁄₁₆ of a pint or 1⁄₁₂₈ 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 about 28.4 mL. The US gallon is defined as exactly 231 cubic inches, making the US fluid ounce about 29.6 mL. The US fluid ounce is about 4% larger than the imperial ounce. The fluid ounce is distinct from the ounce, which measures mass. However, the fluid ounce is sometimes referred to simply as an "ounce" in applications where the volumetric "fluid ounce" is implied by context.