Measuring cups are used in cooking to measure accurate portion sizes of liquid and dry ingredients in recipes. Most are made from metal, glass, or plastic and use the standard 8 ounce (236.5 ml) "cup" as the basic unit of measurement. If measurements are made in US or imperial measurements (cups, teaspoons, etc.), then it is important to use the proper cups when dealing with both dry and liquid ingredient lists. A cup of flour is not measured in the same way as a cup of vegetable oil is, so cooks usually keep two sets on hand. Dry measurements are usually made in plastic or metal containers, while liquids may be measured in transparent glass or plastic cups.
One important thing to keep in mind when using measuring cups is to use the size closest to the recipe's requirements. A typical set marks off many gradations, starting with a 1/8 cup measurement (similar to a tablespoon) and working through the common fractions found in recipes: 1/4, 1/3, 1/2, and finally 1 full cup. Any other proportions can be made through a combination of these cup sizes. Liquid measuring cups may be much larger than dry ones, starting with a 1 cup size and working up to nearly a gallon (30.2 l) in some sets. Individual cup sizes may be marked through visible lines imprinted on the sides of a large capacity measuring cup.
Cooks should note that, in most US recipes, dry measurements are made by volume rather than by mass. This can be confusing to people who are used to measuring ingredients in metric, since 1 cup of flour does not have the same mass as 1 cup of granulated sugar — this volume of flour weighs 120 grams, while a cup of sugar weighs 200 grams. Many cookbooks and online recipe sites provide conversions for most common ingredients.
Recipe measurements usually include important information about which measuring cups to use and how the ingredients should be packed in them. Unlike teaspoon measurements, which may include words like "rounded" or "heaping," dry ingredients are assumed to be level. Some ingredients, such as brown sugar, may have to be packed tightly for accurate measure, while others, such as flour, may need to be sifted for a lighter volume. Liquid measuring cups assume the level of the liquid reaches the desired line at the cook's eye level. Measuring 1 cup (236.5 ml) of water in a 10 cup (2.36 l) container can lead to inaccurate readings, so cooks should try to use the smallest cups possible.
One of the main drawbacks of measuring cups is the number necessary for a complete range of measurements. Cooks must keep at least one complete set of dry cups and another set for liquids. This can require significant storage space, and at least one or two vital cup sizes will often eventually disappear. A modern solution to the storage and shrinkage problem is a universal measuring cup. This kitchen gadget is a two-piece cylinder that acts almost like an open-ended syringe. The outer cylinder contains all the possible gradations of both liquid and dry measurements. A tight-fitting inner cylinder is pulled down to the proper measuring line. The ingredient can then be placed in the container and leveled off. If another ingredient is required, the inner cylinder can be pulled down yet again to add the new measurement. Several dry or liquid ingredients can be added all at once and then dumped as a unit into the mixing bowl or food processor.