My regular bra size is 38DD.  At the recommendation of several reviewers I ordered this bra one size larger in a 40DD-F.  I think a 42 might be better because I had intended this as a sleep bra and the bottom elastic is a bit tighter than I would like in a sleep bra.  However, the real problem is that the cup size runs very small.  If you place your hands over your breasts and press tightly to your chest, you will have an idea of the way this bra supports.  The stretch fabric crushes my boobs to my ribs, creating huge cleavage in the middle and with a surprising amount of overflow ending up at my sides - effectively under my arms.  I think this may be a contributing factor in other reviewers' complaints that the bra is uncomfortable under their arms.  I cannot recommend this bra to full-busted women.  It does immobilize the girls, but not comfortably.