The cup is a customary unit of measurement for volume, used in cooking to measure liquids (fluid measurement) and bulk foods such as granulated sugar (dry measurement). Actual cups used in a household in any country may differ from the cup size used for recipes; standard measuring cups, often calibrated in fluid measure and weights of usual dry ingredients as well as in cups, are available.
As a result of the fact that the imperial cup is actually out of use and the other definitions differ hardly (±3%), the U.S. measuring cups and metric measuring cups may be used as equal in practice.
No matter what size cup is used, the ingredients of a recipe measured with the same size cup will have their volumes in the same proportion to one another. The relative amounts to ingredients measured differently (by weight, or by different measures of volume such as teaspoons, etc.) may be affected by the definitions used.
Metric cup 
|=||162⁄3||international tablespoons (15 mL each)|
|≈||8.80||imperial fluid ounces|
|≈||8.45||U.S. customary fluid ounces|
A "coffee cup" is 1.5 dl, and is occasionally used in recipes.
United States customary cup 
United States customary cup is defined as half a U.S. pint.
|1 U.S. customary cup||=||1⁄16||U.S. customary gallon|
|=||1⁄4||U.S. customary quart|
|=||1⁄2||U.S. customary pint|
|=||8||U.S. customary fluid ounces|
|=||16||U.S. customary tablespoons[nb 1]|
|≈||8.33||imperial fluid ounces|
United States "legal" cup 
|1 U.S. "legal" cup||=||240||millilitres|
|≈||8.12||U.S. customary fluid ounces|
|≈||8.45||imperial fluid ounces|
Imperial cup 
The imperial cup, unofficially defined as half an imperial pint, is rarely found today. It may still appear on older kitchen utensils and in older recipe books.
|1 imperial cup||=||0.5||imperial pints|
|=||10||imperial fluid ounces|
|≈||1.20||U.S. customary cups|
|≈||9.61||U.S. customary fluid ounces|
Japanese cup 
The Japanese cup is currently defined as 200 mL.
|1 Japanese cup||=||200||millilitres|
|≈||7.04||imperial fluid ounces|
|≈||6.76||U.S. customary fluid ounces|
The traditional Japanese cup, the gō, is approximately 180 mL. 10 gō make one shō, the traditional flask size, approximately 1.8 litres. Gō cups are typically used for measuring rice, and sake is typically sold by the cup (180 mL), the bottle (720 mL), and flask (1.8 litre) sizes. Note modern sake bottle sizes are almost the same as the 750 mL American standard for wine bottles, but are divisible into 4 gō.
|1 gō||=||2401⁄13310||litres[nb 3]|
|≈||6.35||imperial fluid ounces|
|≈||6.10||U.S. customary fluid ounces|
Using volume measures to estimate mass 
In Europe, cooking recipes normally state any liquid volume 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. Most recipes in Europe use the millilitre or decilitre (1 dL = 100 mL) as a measure of volume. For example, where an American customary recipe might specify "1 cup of sugar and 2 cups of milk", a European recipe might specify "200 g sugar and 500 mL of milk" (or 0.5 litre or 5 decilitres). Conversion between the two measures must take into account the density of the ingredients. Many European measuring cups have additional scales for common bulk ingredients like sugar, flour, or rice to make the process easier.
|Volume to mass conversions for some common cooking ingredients|
|metric cup||imperial cup||U.S. customary cup|
|water||1[nb 5]||249–250||8.8||283–284||10||236–237||8.3[nb 6]|
See also 
- 1 U.S. customary cup = 16 tablespoons exactly using the old U.S. customary tablespoon of 1⁄2 U.S. fl oz.
- by 1891 definition
- One gram per millilitre is very close to one avoirdupois ounce per fluid ounce: 1 g/mL ≈ 1.002 av oz/imp fl oz This is not a numerical coincidence, but comes from the original definition of the kilogram as the mass of one litre of water, and the imperial gallon as the volume occupied by ten avoirdupois pounds of water. The slight difference is due to water at 4 °C (39 °F) being used for the kilogram, and at 62 °F (17 °C) for the imperial gallon. The U.S. fluid ounce is slightly larger.
- 1 g/mL ≈ 1.043 av oz/U.S. fl oz
- The density of water ranges from about 0.96 to 1.00 g/mL dependent on temperature and pressure. The table above assumes a temperature range 0–30 °C (32–86 °F). The variation is too small to make any difference in cooking.
- Since an imperial cup of water weighs approximately 10 avoirdupois ounces and five imperial cups are approximately equal to six U.S. cups, one U.S. cup of water weighs approximately 81⁄3 avoirdupois ounces.
- (21 CFR 101.9 (b) (5) (viii)
- U.S. Government Printing Office—Electronic Code of Federal Regulations
- U.S. Food and Drug Administration—Guidelines for Determining Metric Equivalents of Household Measures
- In the absence of measuring cups, tablespoons can be used for volume measurement.
- The term international tablespoon as used in this article refers to the 15 mL (~0.5 fl oz) tablespoon used in most countries.
- The Australia tablespoon is defined as 20 mL (~2⁄3 fl oz)
- 1 g/mL is a good rough guide for water-based liquids such as milk (the density of milk is about 1.03–1.04 g/mL).
- 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.