Is 345cc gummy bear under the muscle big enough for 5'6" 120lbs? I would like to be a D in size.

Thank you for your question. You are an excellent candidate for breast
implants and can have significant improvement in your body image and
self confidence. It is much better to accurately discuss
implant volume and projection with an in office exam and detailed
measurements. In order to make an accurate size recommendation, I
would need to assess your chest wall and breast mound
measurements/characteristics. I use these measurements to help me during
the sizing process to guide you to a safe result for your chest wall
and just as important, one that meets your end desires.The next
step is to try on this range of implants in the office with your doctor.
The key to this success is showing your surgeon the body proportion you
desire with a bra sizer and allowing your surgeon to guide you to the
right implant. It will be much easier to communicate in implant cc's
than cup size when determining the appropriate implant for you during
the sizing process. In addition, review of photos and use of
rice bags can be very helpful to the patient and surgeon in achieving a
safe and happy result. Close intereaction and involvement from your
surgeon during this process can help alleviate the anxiety and fears of
choosing the right size. I wish you a safe recovery and fantastic result.Dr. Gill

Thank you for the question. There is no accurate/reliable/predictable correlation between size/profile breast implant utilized and cup size achieved.  Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, and computer imaging) will be critical.  

Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant size/profile selection) is:

1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. For example, I have found that the use of know words such as “natural” or "D cup” etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery, after the use of temporary intraoperative sizers.I hope this (and the attached link, dedicated to breast augmentation surgery concerns) helps. Best wishes for an outcome that you will be very pleased with.