Determining the correct bra size (also known as brassiere measurement or bust size) is the process manufacturers engage in to design and manufacture bras that correctly fit a majority of women, and for individual women, the process of identifying a correctly fitting bra. Bra sizes usually consist of one or more letters indicating the breast cup size and a number, indicating a band size around the individual's torso. Bra cup sizes were invented in 1932 and band sizes became popular in the 1940s. The shape, size, position, symmetry, spacing, firmness, and amount of sagging of individual women's breasts vary considerably. Manufacturers mass-produce bras as ready-to-wear garments and size them to fit standard, idealized, female torsos. Manufacturer's bra size labeling systems vary from country to country because no international standards exist. Even within a single country, one study found that the bra label size was consistently different from the measured size. As a result, about 25% of females have a difficult time finding a properly fitted bra. Some women choose to buy custom-made bras due to the unusual size or shape of their bust.