I usually wear an American XL - 1XL. After reading reviews, I ordered a 3XL . I could not pull it on past my head - much too small. A friend who usually wears a M tried it on, and it fit her. We are both busty. The fabric on the bodice did not stretch side to side across the bust at all. The fabric was oriented so the stretch went up and down instead of side to side.
The quality of the sewing and construction was good, otherwise. Nice color (purple). Had to return it.