# Fluid ounce

A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume equal to 120 of a pint or 1160 of a gallon in the imperial system or 116 of a pint or 1128 of a gallon in the US system. The imperial gallon was originally defined as the volume occupied by 10 pounds avoirdupois of water at 62 degree Fahrenheit, but is currently defined as 4.54609 litres, making the imperial fluid ounce 28.4130625 mL. The US gallon is defined as 231 cubic inches, making the US fluid ounce 29.5735295625 mL, or about 4% larger than the imperial ounce. 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.

## History

The fluid ounce was originally the volume occupied by one ounce of some substance such as wine (in England) or water (in Scotland). The ounce in question varied depending on the system of fluid measure, such as that used for wine versus ale. Various ounces were used over the centuries, including the Tower ounce, troy ounce, ounce avoirdupois, and various ounces used in international trade such as Paris troy. The situation is further complicated by the medieval practice of "allowances" whereby a unit of measure was not necessarily equal to the sum of its parts. For example, the 364-pound woolsack had a 14-pound allowance for the weight of the sack and other packaging materials.[1]

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 and eight pints. Each pint was divided into four gills and twenty fluid ounces, that is, five ounces for each gill. Thus, the mass of an imperial fluid ounce of water is one avoirdupois ounce (28.4 g). The US fluid ounce is based on the US gallon, which is based on the wine gallon, used in England prior to 1824.

## 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 ounce avoirdupois 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 ounce avoirdupois (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.

ml cu in Imp
fl oz
US
fl oz

16.39 1.00 0.58 0.55   1 cu in
28.41 1.73 1.00 0.96   1 Imp fl oz
29.57 1.80 1.04 1.00   1 US fl oz
30.00 1.83 1.06 1.01   "metric fl oz"
50.00 3.05 1.76 1.69
113.65 6.94 4.00 3.84   4 Imp fl oz
115.00 7.02 4.05 3.89
140.00 8.54 4.93 4.73
142.07 8.67 5.00 4.80   5 Imp fl oz
170.00 10.37 5.98 5.75
170.48 10.40 6.00 5.76   6 Imp fl oz
198.89 12.14 7.00 6.73   7 Imp fl oz
200.00 12.20 7.04 6.76
236.59 14.44 8.33 8.00   1/2 US pint
250.00 15.26 8.80 8.45   European beer glass
255.00 15.56 8.97 8.62
255.72 15.60 9.00 8.65   9 Imp fl oz
284.13 17.34 10.00 9.61   1/2 Imp pint
285.00 17.39 10.03 9.64   "metric half pint"
300.00 18.31 10.56 10.14
330.00 20.14 11.61 11.16   European beer bottle
333.00 20.32 11.72 11.26   1/3 litre
340.96 20.81 12.00 11.53   12 Imp fl oz
345.00 21.05 12.14 11.67   "boutique" beer bottle
354.88 21.66 12.49 12.00   12 US fl oz
355.00 21.66 12.49 12.00   "metric 12 US fl oz"
425.00 25.94 14.96 14.37   "metric 3/4 pint"
426.20 26.01 15.00 14.41   3/4 Imp pint
473.18 28.88 16.65 16.00   1 US pint
500.00 30.51 17.60 16.91   1/2 litre
568.26 34.68 20.00 19.22   1 Imp pint
570.00 34.78 20.06 19.27   "metric pint"
738.74 45.08 26.00 24.98   26 Imp fl oz
750.00 45.77 26.40 25.36   3/4 litre
757.68 46.24 26.67 25.62   1/6 Imp gallon
946.35 57.75 33.31 32.00   1 US quart
1,000.00 61.02 35.20 33.81   1 litre
1,136.52 69.35 40.00 38.43   1 Imp quart
1,638.71 100.00 57.67 55.41   100 cu in
1,892.71 115.50 66.61 64.00   1/2 US gallon
2,000.00 122.05 70.39 67.63   2 litres
2,273.05 138.71 80.00 76.86   1/2 Imp gallon
2,458.06 150.00 86.51 83.12   150 cu in
2,500.00 152.56 87.99 84.54   2.5 litres
3,000.00 183.07 105.59 101.44   3 litres
3,277.41 200.00 115.35 110.82   200 cu in
3,785.41 231.00 133.23 128.00   1 US gallon
4,000.00 244.09 140.78 135.26   4 litres
4,096.77 250.00 144.19 138.53   250 cu in
4,546.09 277.42 160.00 153.72   1 Imp gallon
4,916.12 300.00 173.02 166.23   300 cu in
5,000.00 305.12 175.98 169.07   5 litres
5,735.47 350.00 201.86 193.94   350 cu in
6,000.00 366.14 211.17 202.88   6 litres
6,554.83 400.00 230.70 221.65   400 cu in
7,000.00 427.17 246.37 236.70   7 litres
7,374.18 450.00 259.53 249.35   450 cu in
7,570.82 462.00 266.46 256.00   2 US gallons
8,000.00 488.19 281.56 270.51   8 litres
8,193.53 500.00 288.37 277.06   500 cu in
9,000.00 549.21 316.76 304.33   9 litres
9,012.89 550.00 317.21 304.76   550 cu in
9,092.18 554.84 320.00 307.44   2 Imp gallons
9,832.24 600.00 346.05 332.47   600 cu in
10,000.00 610.24 351.95 338.14   10 litres

## References and notes

1. ^ Connor, R. D.; Simpson, Allen David Cumming; Morrison-Low, A. D.; National Museums of Scotland (2004). Weights and measures in Scotland: a European perspective. NMS. p. 153. ISBN 978-1-901663-88-4. Retrieved 21 September 2012.
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. ^ "Food and Drug Administration, HHS" (PDF). Retrieved 2006-04-18.