There is a lot of information, and this page is intended to get you started.
Size Size of the band is a good indicator of what you are actually buying. If you are trying to buy the right size bra, this chart should help. The bands are measured on a 30 band bra and the band itself is measured from the underwires to the underwires at the back of the cup. It is also important to remember that many women's bras are not exactly the same size, so the band size you end up with will vary from a 30 band to a 40 band. Band Size - If you don't know what the size of your bra is, it is wise to measure the underwires first. This is where most of the band is, so you should have your underwires hanging under a measuring tape. The band will usually be about 10mm wide. For most women, this is a perfect fit. If you don't have underwires, measure around the outside of your cup. You want to measure around 2-3 inches from the side seam. This is the band width. If you have a tight band, you may not have enough room. If so, buy a larger cup.