Hi there- If there is one thing I would like to be able to immediately convince every woman interested in breast enhancement of, it is that the best implant for you should NOT be based on your desired bra size, or the number of cc's your friend has, or the way they look outside of your body in your bra... Please understand that to achieve a pleasing long term outcome the implant needs to be chosen based on your body dimensions, your current breast parameters, your desired appearance (not bra size), and your lifestyle. You can read more about this here:
One can only guess at the size following implant placement. Most plastic surgeons can come pretty close to determining the correct size. The difficulty is that all bra manufacturers are a little different. You know this already if you have shopped at different stores and found that you were a "B" at Target, but a "C" at Victoria Secret. In this case, I would guess that you will be in the full "C" or small "D" range. Good Luck!