I wear a 40 DD . I purchased a 2X and it is a perfect fit.
These bras are a very stretchy fabric. You cant expect them to be like a structured regular type bra. Sorta like the difference between regular jeans or leggings.
I love these bras. If you are wearing a tight or very fitted top you might want to wear a regular bra but for most other clothes I find I can wear these bras. I am 54 and age 67. Nursed 3 children , so my breasts are pretty heavy and not young by any means, but these bras are very comfortable and I am wearing them day and night.
I give them a 5 star.