Cup size refers to the measurement used to indicate the volume of a woman's breast in relation to her band size, which is the measurement around her chest. It is commonly represented by letters, such as A, B, C, and so on, with each letter representing a specific increase in breast volume. The cup size is determined by the difference between the band size and the bust measurement. For example, if a woman has a band size of 34 inches and a bust measurement of 36 inches, the difference is 2 inches, which typically corresponds to a B cup size. Cup sizes can vary between different brands and styles of bras, so it is important for individuals to try on various sizes to find the best fit.