Don't buy if you're an A cup.
It really is VERY stretchy. I'm a size sixteen, I don't like tight clothes, but I bought a twelve going by the reviews, and it's still a little loose. Somehow I don't fill the cups despite getting two sizes down- which are also flappy at the top and lack any underwire to hold their shape. It was surprisingly difficult to adjust the straps as well. It looks cute, it's a nice thick material with a firm zipper, but it's really hard to get it to fit properly. Be prepared to sew in your own extra straps, padding, or underwire.