# Fluid ounce

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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).

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 ≈ 1.055852392 imperial fluid ounces ^{[2]}≈ 1.014420681 U.S. customary fluid ounces ^{[3]}^{[4]}≈ 1.830712323 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

- ↑ 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.
- ↑
^{2.0}^{2.1}"The Units of Measurement Regulations 1995". 2000-09-20. Retrieved 2006-04-18. - ↑
^{3.0}^{3.1}One U.S. gallon is defined as 231 cubic inches. - ↑
^{4.0}^{4.1}^{4.2}This assumes the international inch of exactly 25.4 millimetres. - ↑ "Food and Drug Administration, HHS" (PDF). Retrieved 2006-04-18.

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