# Fluid ounce

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Fluid ounce

A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is a unit of volume equal to about 28.4 mL in the imperial system or about 29.6 mL in the US system. 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.

In 1824 the British Parliament defined the imperial gallon as the volume of ten avoirdupois pounds of water. The gallon was divided into four quarts or eight pints. Each pint was divided into four gills or twenty fluid ounces. Thus, the mass of an imperial fluid ounce of water is one avoirdupois ounce (28.4 g) The US ounce is based on the earlier definition of one gallon equaling 231 cubic inches. This measurement at first glance does not seem to have any tie to mass, however it is believed[by whom?] to have come from a previous measure of a gallon as being 224 cubic inches (just 7 cubic inches less, both numbers being multiples of 7) which was used because it was the exact volume of 8 pounds of wine.[1] Thus one pint of a wine gallon is equal to the volume of one pound of wine, and there are 16 fluid ounces in a pint, just as there are 16 ounces in a pound. Subdivisions of the US gallon are similar to those of the imperial gallon the difference being that there are only four ounces to the gill (sixteen to the pint or 128 to the gallon). Thus the US fluid ounce is about 4% larger than the imperial ounce.

## Definitions and equivalences

Imperial fluid ounce
 1 imperial fluid ounce = 1⁄160 imperial gallon = 1⁄20 imperial pint = 1⁄5 imperial gill = 8 imperial fluid drams ≈ 28.4130625 millilitres[2] (cm3) ≈ 1.733871455 cubic inches = 1 avoirdupois ounce of water at 62 °F (16.7 °C)[3] ≈ 0.960759940 US fluid ounce
US customary fluid ounce
 1 US fluid ounce = 1⁄128 US gallon = 1⁄32 US quart = 1⁄16 US pint = 1⁄8 US cup = 1⁄4 US gill = 2 tablespoons = 6 teaspoons = 8 US fluid drams ≈ 1.8046875 cubic inches[4] ≡ 29.5735295625 millilitres (or the same number of cubic centimetres (cm³)) ≈ 1.040842731 imperial fluid ounces ≈ 1.041 avoirdupois ounce (29.5 g) of water at 62 °F (16.7 °C)
US food labelling fluid ounce
US regulation 21 CFR 101.9(b)(5)(viii) also defines a fluid ounce as exactly 30 millilitres, but this is for use in nutrition labeling only.[5]
 30 millilitres ≈ 1.05585 imperial fluid ounces[2] ≈ 1.01442 US customary fluid ounces[4] ≈ 1.83071 cubic inches
Other useful conversions

Given the definitions above, the number of US fluid ounces in one litre is:

1 fl oz29.57353 ml × 1000 mll = 33.8140 fl ozl

There are thus about 34 customary US fluid ounces in one litre.

Similarly, there are exactly 33 13 US food-labelling fluid ounces in a litre.

## References and notes

1. ^ Rowlett, Russ (September 13, 2001). "Gallon". How Many? A Dictionary of Units of Measurement. University of North Carolina at Chapel Hill. Retrieved 2010-10-31.
2. ^ a b "The Units of Measurement Regulations 1995 (Schedule)". 2000-09-20. Retrieved 2006-04-18.
3. ^ The imperial gallon was originally defined as the volume occupied by ten avoirdupois pounds of water at 62 °F (16.7 °C), weighed in air with brass weights.
4. ^ a b One US gallon is defined as 231 cubic inches.
5. ^

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### Look at other dictionaries:

• Fluid ounce — Fluid Flu id, n. A fluid substance; a body whose particles move easily among themselves. [1913 Webster] Note: Fluid is a generic term, including liquids and gases as species. Water, air, and steam are fluids. By analogy, the term was sometimes… …   The Collaborative International Dictionary of English

• Fluid ounce — Ounce Ounce (ouns), n. [F. once, fr. L. uncia a twelfth, the twelfth part of a pound or of a foot: cf. Gr. o gkos bulk, mass, atom. Cf. 2d {Inch}, {Oke}.] 1. A weight, the sixteenth part of a pound avoirdupois, and containing 28.35 grams or… …   The Collaborative International Dictionary of English

• Fluid ounce — (Flüssigunze) ist eine Maßeinheit des Raums (Flüssigkeit, Apothekermaß), die vor allem in Nordamerika gebräuchlich ist. Das Einheitenzeichen ist Imp.fl.oz. oder US fl.oz. Imperial fluid ounce 1 Imp.fl.oz.  =  8 Imp.fl.dr. =  480… …   Deutsch Wikipedia

• fluid ounce — n 1) a U.S. unit of liquid capacity equal to 1/16 pint 2) a British unit of liquid capacity equal to 1/20 pint * * * (fl oz) a unit of capacity (liquid measure) of the apothecaries system, in the United States being 8 fluid drams, one sixteenth… …   Medical dictionary

• fluid ounce — [flo͞o΄id ouns′] a unit of liquid measure, equal to 1/ 4 gill or 1/ 16 pint or 8 fluid drams (29.5734 milliliters): the British and Canadian imperial fluid ounce equals 1/ 20 of an imperial pint or 28.4122 milliliters: abbrev. fl oz …   English World dictionary

• fluid ounce — fluid ounces N COUNT: num N, oft N of n A fluid ounce is a measurement of liquid. There are twenty fluid ounces in a British pint, and sixteen in an American pint …   English dictionary

• fluid ounce — noun count a unit for measuring an amount of liquid, equal to .02957 liters. There are 16 fluid ounces in a PINT …   Usage of the words and phrases in modern English

• fluid ounce — n written abbreviation fl oz a unit for measuring liquid, equal to 1/20 ↑pint or 0.028 litres in Britain, and 1/16 pint or 0.030 litres in the US …   Dictionary of contemporary English

• fluid ounce — ► NOUN 1) Brit. a unit of capacity equal to one twentieth of a pint (approximately 0.028 litre). 2) (also fluidounce) US a unit of capacity equal to one sixteenth of a US pint (approximately 0.03 litre) …   English terms dictionary

• fluid ounce — (fl oz)    a traditional unit of liquid volume, called the fluid ounce to avoid confusion with the weight ounce. In the U. S. customary system there are 16 fluid ounces in a pint, so each fluid ounce represents 1.804 687 cubic inches or 29.573… …   Dictionary of units of measurement