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A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl.) is a unit of volume equal to about 29.57  ml, in the US. It is used in both the imperial and the US customary systems, and it is sometimes referred to simply as an ounce in cases where no confusion with the unit of weight (also called an ounce) is likely to occur.

[edit] 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[1] (cm³)
	≈	1.733871455	cubic inches
	=	1	avoirdupois ounce of water at 62 °F (16.7 °C)[2]
	≈	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
	≈	1.80468754	cubic inches[3]
	≈	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 labeling 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.^[4] 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[1]
	≈	1.014420681	US customary fluid ounces[3]
	≈	1.830712323	cubic inches

Other useful conversions

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

^{1 fl oz}⁄_{29.57353 ml} × 1000 ^ml⁄_l = 33.8140 ^{fl oz}⁄_l

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

Similarly, there are exactly 33 ¹⁄₃ US food-labelling fluid ounces in a litre.

[edit] References and notes