Will 420cc Silicone Implants Leave Me with Boobs Too Big?

         420 cc may take an A cup to a C cup or possibly a small D cup.  For a DD cup, this may take 600 cc or more.  Find a plastic surgeon with ELITE credentials who performs hundreds of breast augmentations each year.  Then look at the plastic surgeon's website before and after photo galleries to get a sense of who can deliver the results.  Kenneth Hughes, MD Los Angeles, CA

In order to make an accurate size recommendation, I would need to assess your chest wall and breast mound measurements and characteristics.  Unfortunately, there is not a general rule of thumb or objective criteria to implant selection.
Your plastic surgeon will perform several measurements of your chest wall and breast anatomy and determine a range of implants that both fit your chest wall and reach your desired goals.
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.
I wish you a safe recovery and fantastic result.
Dr. Gill

Make sure you are comfortable with the size implants you will be getting before you get to the operating room.  You should retry the sizes to see how you look.  Bra sizes are not uniform from manufacturer to manufacturer, so don't get caught up wanting a certain cup size ( I.e. a D in Victoria secret may be a C in Playtex).

If you have had a significant size change, a revisit of sizing is needed. Since you have question, it is advisable anyway.

I like to have patients try on implant sizers in the office and use that info as part of the decision process. Since there are no uniform standard for cup size, I find the letters not helpful. Some surgeons as a guideline suggest about one cup size increase for each 150-200 cc of implant. 

Best wishes for a nice outcome.