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The cup is a unit of measurement for volume, used in cooking to measure bulk foods, such as chopped vegetables (dry measurement), and liquids (fluid measurement). It is in common use in many countries, especially those that were part of the British Empire, including the United States and most members of the Commonwealth of Nations, and nations that were influenced by them, such as Japan. The cup is not commonly used in the United Kingdom and the rest of Europe.

There is no internationally agreed standard definition of the cup, largely because different English-speaking nations have diverged in the laws that define their next smaller unit of volume, the fluid ounce, and most other countries use metric measuring cups and millilitres instead. Consequently, the cup volume ranges between 1/5 (0.20) and 1/4 (0.25) of a litre (200–250 millilitres). By comparison, the difference in the legal fluid ounce is relatively insignificant for household purposes; the difference is only about 4%.

Recipes in cookbooks naturally use the local customary units; but, because the cups used in the Commonwealth of Nations and the United States differ by only ½ (0.5) fluid ounce, the respective measures are close enough for cooking.

• 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, 1.8 litres. Sake is typically sold by both the cup (180 mL) and flask (1.8 litre) 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 litre 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 U.S. fluid ounces, equivalent to approximately 237 millilitres or 8.3 Imperial fluid ounces.

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

In metric regions, cooking recipes normally state any liquid volumes larger than a few tablespoons in millilitres, the scale found on most measuring cups worldwide. Non-liquid ingredients are normally weighed in grams instead, using a kitchen scale, rather than measured in cups. Some recipes in Europe use the decilitre (1 dL = 100 mL) as a cup-like measure. For example, where an American customary recipe might specify "1 cup of sugar and 2 cups of milk", a metric recipe might specify "200 g sugar and 500 mL of milk" (or ½ litre or 5 decilitres). Conversion between the two measures must take into account the density of the ingredients (granulated sugar, 0.8 g/mL; wheat flour, 0.5–0.6 g/mL; table salt, 1.2 g/mL^[1]).

• The Imperial cup and the U.S. cup are each 1/2 of their respective pints. But, because of the difference in the definition of a U.S. gallon and an Imperial gallon, from which the lower 'wet measures' are derived, an Imperial cup is greater than a U.S. cup.

• An Imperial fluid ounce is defined as "the volume occupied by one avoirdupois ounce of water at 62 °F (16.7 °C)": one Imperial fluid ounce weighs one avoirdupois ounce. Thus an Imperial cup of water (10 Imperial fluid ounces) weighs 10 avoirdupois ounces. A U.S. fluid ounce is 1.04 avoirdupois ounces, so a customary cup of water (8 U.S. fluid ounces) weighs 8.32 avoirdupois ounces and is 16.8% less than an Imperial cup of water in terms of mass. The above equivalence only holds for water; for cups of other substances, their mass will depend of their densities.

• In the absence of measuring cups, tablespoons can be used: 16 tablespoons equal a cup, at a rate of 1 tablespoon to ½ a fluid ounce.

1. ^ L. Fulton, E. Matthews, C. Davis: Average weight of a measured cup of various foods. Home Economics Research Report No. 41, Agricultural Research Service, United States Department of Agriculture, Washington, DC, 1977.

• Measuring cup