I'm 5'4" and usually fit into a medium. I got a size larger and it fits nicely. I also have a small chest. I probably wouldn't recommend it for people who have larger chests, because the top part runs a little small.
I'm a triple d and the covering for the chest don't quite cover it 😂 it looks fine with a bralette but also is very difficult to put on. It's very cute though and looks just like the picture, I recommend this product