Cup (unit)

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The cup is a unit of measurement for volume, used in cooking to measure bulk foods like chopped vegetables (an example of a dry measurement) or liquids like milk (fluid measurement). It is in common use in many countries, especially nations which were once part of the British Empire, including the United States and most members of the Commonwealth of Nations, and nations which sought to emulate them, such as Japan. However the "cup" is not commonly used in the UK.

There is, however, no internationally agreed upon standard definition of the cup, largely because different nations have diverged in the laws which defined the more basic unit, the fluid ounce. Consequently, its volume ranges between 1/5 (0.20) and 1/4 (0.25) of a litre (200 — 250 mL) in the metric system, the international standard measurement system. By comparison, the difference in the legal fluid ounce is relatively insignificant for household purposes as the ratiometric difference in volume is only about 4%.

Recipes in cookbooks will naturally use their local customary units, but since the cups used in the Commonwealth of Nations and the United States differ by only ½ (0.5) fl oz, the respective measures are close enough for cooking purposes.

Australia, Canada, New Zealand: one cup is 1/4 litre (250 mL), equivalent to approximately 8.8 Imperial or 8.5 U.S. fluid ounces.

Japan: one cup is 1/5 litre (200 mL). A traditional Japanese cup (gō) is 180 ml; 10 Japanese cups together make one shou, the traditional flask size, of 1.8 liter. Sake is typically sold by both the cup (180 ml) and flask (1.8 liter) sizes. The cup size used for measuring rice is the traditional size of 180 ml. (For example, a 10-cup rice cooker has a capacity of 1.8 liter or 1 shou.) [1]

United States (current legal definition, such as for nutrition labeling): one cup is 240 mL, as defined in U.S. law (21 CFR 101.9 (b) (5) (viii)). [2] [3]

United States (customary definition): one cup is 0.5 U.S. pints, or 8.0 fl oz (U.S.) fluid ounces, equivalent to approximately 237 milliliters or 8.3 Imperial fluid ounces.

Cup sizes implied in cooking recipes do not necessarily define serving sizes for beverages. For example, a cup of brewed coffee in the U.S. is traditionally 6 U.S. fluid ounces (180 mL) instead.

Metric recipes in Europe often use the deciliter (1 dl = 100 ml) as a cup-like measure. For example, where an American customary recipe might specify "2 cups", a metric recipe might specify "5 deciliters".

[edit] Equivalence with other units of volume

1 Cup (Assuming 1 Cup = 240 ml) is equal to:

240 milliliters
0.24 Litres
8.11536541 US fl oz
240 Cubic centimeters
0.0634012923 US gallons

[edit] Equivalence with units of weight and mass

Both an Imperial cup and a US cup are 1/2 of their respective pints. However due to the difference in the definition of a US gallon and an Imperial gallon, from which the lower 'wet measures' are derived, an Imperial cup is greater than a US cup.

An Imperial fluid ounce is defined as 'the volume occupied by one avoirdupois ounce of water at 62 °F (16.7 °C)' i.e. one Imperial fluid ounce weighs one avoirdupois ounce. Thus an Imperial cup of water, at 10 Imperial fluid ounces (1/2 an Imperial Pint), also weighs 10 ounces. A US fluid ounce is 1.04 avoirdupois ounces so a customary cup at 8 US fl oz weighs 8.32 oz and is 16.8% less than an Imperial cup in terms of mass.