A good rule of thumb: A well-fitting bra should sit flat in the gore (the center connecting piece of the bra). If it’s too wide for your chest, the gore will buckle or push out, which could cause the underwire to dig in over time. Always make sure the gore is right up against your sternum. If it’s not, then go up a cup size until it does. If you have close-set breasts, look for a narrow gore with minimal separation.