Note that the measurements in this section are in U.S. customary units.
Measures are classified as either dry measures or fluid measures. Fluid measures are measures of volume, while dry measures are measures of weight. Whether the ingredient you are measuring is dry or fluid really doesn't matter, and will only confuse you. Simply use the measure that is specified in your recipe.
U.S. recipes are almost always in terms of volume.
In domestic cooking, bulk solids, notably flour and sugar, are measured by volume, often cups, though they are sold by weight at retail. Weight measures are used for meats and butter; butter is sold by weight but in packages marked to facilitate common divisions by eye. (As a sub-packaged unit, a stick of butter, at 1/4 lb, is a de facto measure in the U.S.)
Cookbooks in Canada use the same system, although pints and gallons would be taken as their Imperial quantities unless specified otherwise. Following the popularization of the metric system, recipies in Canada are frequently published with metric conversions.
Note that measurements in this section are in Imperial units
Traditional British measures distinguish between weight and volume.
The "cup" is little used as a measure in the UK, although the practised cook will be aware of it from reading American recipes. Older recipes may well give measurements in cups; in so far as a standard cup was used, it was usually half a pint (sometimes a third of a pint), but if the recipe is one that has been handed down in a family, it is just as likely to refer to someone's favourite kitchen cup as to that standard.
American cooks using British recipes, and vice versa, need to be careful with pints and fluid ounces. A US pint is 473 ml, while a UK pint is 568 ml, a fifth larger. A US fluid ounce is 1/16 of a US pint (29.4 ml); a UK fluid ounce is 1/20th of a UK pint (28.4 ml).
On a larger scale, perhaps for institutional cookery, it must be noted that an imperial gallon is eight 20 imperial fl oz pints (4.54 liters) whereas the US gallon is eight 16 US fl oz pints (3.78 liters).
The Metrication in the UK for most purposes, some decades ago, and both taught in schools and used in books. It is now mandatory for the sale of food. However, a very large part of the population continues to use Imperial measures. Most modern cookery books give ingredients in both units.
In the rest of the world, recipes use the SI system of litres (l) and millilitres (ml), grams (g) and kilograms (kg), and degrees Celsius (°C).
In addition to these, some measures are often redefined in terms of metric units. Most countries use the following units:
However, Australian recipes use a 15 ml dessertspoon and a 20 ml tablespoon. And in New Zealand, at least, a pint may be approximated as 600 ml.
You will sometimes encounter additional instructions that are required to get the correct amount of the ingredient. For example, a recipe might call for "1 cup brown sugar, firmly packed", or "2 heaping cups flour." If you encounter one of these special requests, consult the table below:
Some conversion tables: http://www.dictionary.com/search?q=measurement