What is the biggest size for breast implants under the muscle? How many cc? 4000cc?

The size you are talking about is way out of the normal range of implants. You have to discuss this with your plastic surgeon and get an evaluation and determination of what size of implants could fit on her chest wall. And yes, you probably would have to go above the muscle.

Thank you for sharing your excellent question.  The largest silicone implants currently available are 800cc while saline implants can be overfilled to reach sizes in excess of 2000cc.  Hope this helps.

The largest saline breast implant available in the U.S. is 960 cc's.  The largest silicone implant one can get in the US is 800cc.  In general after a period of time, which is variable, larger breast implants can be placed due to tissue stretch.  Two years should allow you to go bigger by at least 100 cc maybe larger.  Choosing an implant based on an aesthetic goal that exceeds your anatomic capacity may lead to complications and possibly revision.

I had to double check to see if you said 400 or  4000.   I don’t even know if you can get a 4000 cc implants. I would never put in implants even close to that . You're talking almost 10 pounds a side.   if you go to enough surgeons you’ll probably find someone to do it but I advise against it.

Dear Plasticlover7,
breast implant type and sizing selection is a complicated process and requires a detailed consultation that includes a discussion of your goals, a detailed examination, and a lengthy discussion. But the decision will always start and end with the patient. When it comes to sizing, we have all of our patients find 3 photos of their desired breast size. We ask for naked breast photos because clothing can obscure the true size (push up bras). Next, we consult with patients and go over the photos and take detailed breast measurements during a physical exam. Next, we using a sizing algorithm to determine a range of implants that will work based on the exam and the measurements.Lastly, during the operation, we use silicone sizers in the operating room to see how the size actually looks in the breast. We sit the patient up in the operating room, while asleep of course, and compare the sizer result with their desired look photos. If it is too small, we start the process over with a slightly larger implant. We don't stop until we get the perfect match.Of all of my breast augmentation patients, every one of them has been happy with their size due to this detailed and meticulous process. You don't want to invest time and money into a result that is either too big or too small.You should discuss your concerns with a board-certified plastic surgeon and make sure that your surgeon understands your goals.
Daniel Barrett, MD

You need a formal evaluation by a licensed plastic surgeon and expert in breast augmentations to determine what is best for you and your goals.Proper breast enlargement is not a "cookie-cutter" procedure where the same technique is applied to every patient. Every woman who comes to my practice has unique needs and different goals for her breast augmentation. As a board-certified plastic surgeon, I always listen carefully to each woman's concerns and thoroughly discuss the key points of the procedure. I also take into account their overall height and weight, the size and shape of the underlying chest and ribcage, the tightness and elasticity of the skin, and the amount of natural breast tissue. Prior to the procedure, we discuss and make decisions regarding location of the incision, whether to place the implant under or over the chest muscle, and what type of implant to use (I offer multiple types of silicone gel breast implants, as well as saline implants).
My experience performing thousands of aesthetic breast surgeries in a wide anatomical range of patients enables me to achieve consistently beautiful and natural results that are customized to each patient’s body type and goals. These results are the product of extensive communication, meticulous planning, and skillfully executed surgery.
I suggest consulting with a board-certified plastic surgeon and expert in Breast Augmentation surgeries. - Dr. Cohen

I must say that I have never heard of a breast implant being this large, whether it is a saline or silicone implant!  Very few massive breast reductions have ever been this large as well!  Balance and symmetry with your overall body shape is what this procedure should be about.  Choose a very good Plastic Surgeon and follow the advice of his or her recommendation to decide what makes sense for you.Good luck to you.Frank Rieger M.D.  Tampa Plastic Surgeon