Keep in mind that this bra has a lot of stretch and the measurements below are basic guidelines. We suggest going with the size that's closest to your bust measurement as the cup can be a little more flexible. For example, if you're a 34D we'd suggest a size 3. This is because the 4 will be too large in the bust, but a 2 will be too small in the cup. Any questions, just ask! Bra sizing can be tough and we just love talking about boobs.