Bra size indicates the size characteristics of a bra to accurately fit the breasts. While there are a number of bra sizing systems in use around the world, the bra sizes usually consist of a number, indicating the size of the band around the torso, and one or more letters that indicate the breast cup size. Bra cup sizes were invented in 1932 while band sizes became popular in the 1940s. For convenience, because of the impracticality of determining the size dimensions of each breast, the volume of the bra cup, or cup size, is based on the difference between band length and over-the-bust measurement.