1. There is a misconception about bra sizes. People think that D is a big size and, therefore, DD is huge - but this is not necessarily true. Fifty per cent of women are a size D or bigger.
2. The size of the cup is in relation to the back size. A 36D is a cup bigger then a 34D. There are more than 100 sizes of bras.
3. Many women don't know how a bra should fit and therefore don't even know that they wearing the wrong size. There are several ways to tell if your bra is fitting correctly and a good bra fitter can explain how to do this. Take a look at the section titled "Your bra doesn't fit you properly if..."
4. Women's bodies change size all the time, and while they may change their dress size, they don't realize that they may need a new bra size as well. Weight gain, weight loss, childbirth, stress all contribute to changing bra sizes.
5. Many stores carry limited sizes of bras, eliminating the choice of getting the right size for most women. This is particularly true when women don't know what they are getting is wrong.