Bra size is a measurement used to determine the fit of a bra, which supports the breasts. It consists of two parts: a number and a letter. The number represents the band size, which is the measurement around the torso just under the bust, while the letter indicates the cup size, which reflects the volume of the breast. To find the correct bra size, individuals typically measure their band size and bust size, then use a sizing chart to determine the appropriate size. Proper fitting is important for comfort and support, as an ill-fitting bra can lead to discomfort and health issues.