A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is a unit of volume in both the imperial and the US customary systems. It is common to refer to the unit simply as an ounce, especially in cases where no confusion with the unit of mass is likely to occur.
Definitions
- Imperial fluid ounce
- The imperial fluid ounce is 1⁄160 of an imperial gallon making it very nearly the volume occupied by one avoirdupois ounce of water.[1]
-
-
1 imperial fluid ounce = 1/160 imperial gallons = 1/20 imperial pints = 1/5 imperial gills = 8 imperial fluid drams = 28.4130625 millilitres (exactly)[2] ≈ 1.733871455 cubic inches ≈ 0.960759940 U.S. fluid ounces
-
- U.S. customary fluid ounce
- The U.S. customary fluid ounce is defined to be 1⁄128 of a U.S. gallon. This volume of cool, pure water weighs about 1.04 avoirdupois ounces (29.5 g).
- U.S. food labelling fluid ounce
- U.S. regulation 21 CFR 101.9(b)(5)(viii) also defines a fluid ounce as exactly 30 millilitres, but this is for use in nutrition labelling only.[5] This is not meant to concur with the customary US definition exactly but is a common source of confusion.
References and notes
- ^ The imperial gallon was originally defined as the volume occupied by ten avoirdupois pounds at 62 °F (16.7 °C), weighed in air with brass weights.
- ^ a b The Units of Measurement Regulations 1995 (2000-09-20). Retrieved on 2006-04-18.
- ^ a b One U.S. gallon is defined as 231 cubic inches.
- ^ a b c This assumes the international inch of exactly 25.4 millimetres.
- ^ Food and Drug Administration, HHS (PDF). Retrieved on 2006-04-18.
