# Fluid ounce

Template:Wiktionarypar 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 ​1160 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 ​1128 of a U.S. gallon. This volume of cool, pure water weighs about 1.04 avoirdupois ounces (29.5 g).
 1 U.S. fluid ounce = 1/128 U.S. gallon = 1/16 U.S. pints = 1/4 U.S. gills = 8 U.S. fluid drams = 1.8046875 cubic inches (exactly)[3] = 29.5735295625 millilitres (exactly)[4] ≈ 1.040842731 imperial fluid ounces
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.[citation needed]
 30 millilitres ≈ 1.05585 imperial fluid ounces[2] ≈ 1.01442 U.S. customary fluid ounces[3][4] ≈ 1.83071 cubic inches[4]

Other Useful Conversions

Given the definitions above, we can calculate how many US fluid ounces are in one liter:

1/29.5735295625 * 1000 = 33.8140

There are thus about 34 fluid ounces in one liter.

## References and notes

1. 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.
2. "The Units of Measurement Regulations 1995". 2000-09-20. Retrieved 2006-04-18.
3. One U.S. gallon is defined as 231 cubic inches.
4. This assumes the international inch of exactly 25.4 millimetres.
5. "Food and Drug Administration, HHS" (PDF). Retrieved 2006-04-18.