Calculate your cup size: Take your band measurement that you calculated in step 1 and subtract it from your bust measurement. Use that number to determine cup size: 1=A, 2=B, 3=C, 4=D, 5=DD or E ...

It’s long been touted that 80% of women wear the wrong bra size. We talked to an expert to help you find out if you might be one of them.

Basically, they are sizing groups, equivalent to bra sizes, that are based on cup volume. And the volume of cup size varies with the band width. It's easy to calculate your sister bra size.