OMG plz forgive my late reply, I have been away. I did some measurements and just the bust area lying flat is about 17.5". Each of the bust compartments (haha don't know how to describe it) is 11 ". I wear a size M so it's a bit hard to make any recommendations for this shirt. There is alot of room for the bust.
Ahh I wish i could tell. Each bust cup measures 11". Measurement just under the bust lying flat is 17.5". It has elastic in the back so there is lots of stretch.