Brassiere measurement (also called brassiere sizes, colloquially bra sizes or bust sizes) refers to determining what size of bra a woman wears and mass producing bras that will fit most women. Bra sizes usually consist of a number, indicating a band size around the woman's torso, and one or more alphabetical letters indicating the breast cup size. Bra cup sizes were invented in 1932 and band sizes became popular in the 1940s.
Bra sizing systems are typically used to label off-the-shelf bras and are not used for custom-made bras or bras built into other garments. Bra size labeling systems vary from country to country while manufacturers do not adhere to international standards. Some manufacturers have been found to deliberately mis-state the band size. One study found that the label size was consistently different from the measured size. Furthermore, the shape, size, symmetry, and spacing of women's breasts vary considerably, and can differ greatly from the standard off-the-shelf bra shapes and sizes, especially if the breasts have been augmented, are tubular shaped, or if they sag.
Bra-fitting methods, originally conceived in the 1930s, are only accurate for up to about U.S. size 38D. Larger-breasted women cannot depend on them for accurate measurements. Bra-fitting instructions uniformly require women seeking to find a correctly fitting bra to already own one. Even professional bra fitters may disagree on the correct size for the same woman. As a result, more than 80% of women wear an incorrect bra size.
Read more about Bra Sizes: Measurement Method Origins, Correct Fitting, Measurement Difficulties, Measurement Methods, Research, Advertising and Retail Influence, International Fitting Standards, Calculating Cup Volume and Breast Weight