Like most clothes, bras (brassieres) come in different sizes. But the sizing system can be quite confusing for men as it involves seemingly random digits and some “obvious” lettering grade, such as 34C.
The bra size gives away two pieces of information: band size and cup size.
Band size is the circumference of the woman’s ribcage, not accounting for the breasts. Each brand measures band size differently, but usually the measuring tape is placed around the woman’s torso under the breast where the skin folds, while some companies measure above the breasts. The number refers to the band size in inches, centimetre or dress size (e.g. 34″ = 75cm = size 10). A similar number is bust size, which includes the breasts. This is measured with the measuring tape around the torso and the fullest point of the breasts.
The letter in the sizing refers to the cup size, which describes the breast volume. This is calculated by taking the difference between the bust size and the band size. For example, if a woman’s bust size is 36 inches and her band size is 34 inches, the difference is 2 inches and therefore, her cup size is C (UK system, in the US, it would be a B). The corollary to this is that a size “D” does not necessarily mean the woman has big breasts. A 28D will not be much bigger than a 32B, but the breasts will be bigger compared to the torso. In fact, band size will typically affect actual breast size more than the cup size. Cup size measurement differs depending on the country, with the US system being 1 inch larger. The following is a table showing what each cup size letter refers to:
Bra size is not an exact science as there are many other factors such as physical constitution, breast shape, asymmetry and pendulousness. Some surveys show that up to 80% of store bra fittings result in poor fit, showing how difficult it is for women to even know their own proper bra size. As for men looking to buy a bra for their significant other, it will probably save you much effort and brainpower asking them instead of trying to work it out yourself.