You need to consider a couple of things to correctly measure for your bra size. First to determine the band size measure across the top of your chest and under your arms. If this number comes out an even number this will be your band size, if not add 1 to your results for correct band size. You will then need to measure for your cup size by measuring around the back to the fullest part of the bust. The next step to determine your cup size is to subtract the fullest bust measurement from the band measurement to get the difference. The size of the cup needed is equal to one inch and if there is a one inch difference the cup size would be an A; two inch difference a B; three inch difference a C and so on. You will need to try a variety of bras in this size to make sure they are a comfortable fit for you.