When I tried on my dress at David's Bridal they supplied the corset bra and bridal slip. They put me in a 36 D corset bra. I am a 34 B regular. She said she was going with the D for the waist. Admittedly I don't know much about various bra sizes. I thought the letters were more about cup size and the numbers were for waste. The 36 D was good around my waste. It did cinch me in. However the cups were WAY to big. I left with my dress and my bridal slip but I didn't purchase the corset bra from them because I was unsure as to what size to get. I was thinking 36 but go with a B cup. Anyone have advice? I live in a small town and don't have a lingerie shop in my town. I wanted to get the proper bra prior to getting my dress altered.