Is 400cc silicone under the muscle huge for someone who is 5ft and 115 lbs?

I agree with others that an exact measurement of your breast and body characteristics is crucial to determine the size of a breast implant, but, in my opinion, based on your height and weight, the size implant you mention is way too large and can significantly increase your risk of complications. Hope this helps. 

400cc in some patients fits well.  However, you are fairly petite by the sounds of it and the implant is likely going to look fairly large.  Whether that matches your goals or not is hard to say.  It doesn't make sense that your surgeon would just pick a size for you and expect that you will like it.  How can they know what you want?  I do about 4 different things to get the perfect implant for someone.  Two things I would recommend to you are trialling sizers at your surgeons office in a bra with no padding (or using flour in a baggy instead) to see the range of implants that look good.  The other thing is to take some photos of ideal breasts and then some breasts that are close but just a bit off.  I have my patients do this so that I can chose just the perfect implant to match their goal during breast augmentation surgery.Dr Rodger ShorttOakville Plastic Surgeon Assistant Clinical Professor &Director of Cosmetic Surgery Training,McMaster UniversityPerforming plastic surgery for Oakville, Mississauga, Burlington, Georgetown, Milton, Hamilton and Toronto.

Hello and thank you for your question. This is a question which can most accurately be answered with an in-person consultation.  The best implant size depends on your individual breast anatomy and measurements.  The most important aspect is to find
a surgeon you are comfortable with.  I recommend that you seek consultation with a
qualified board-certified plastic surgeon who can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

It's all relative but you should have been able to see what it looks like either by "trying it on" with implant sizers or through a virtual preview as with something like vectra. If you walked into the office, were told to get 400s and then they took your deposit without even letting you see what things would look like I'd take that as a big red flag. Best of luck! 

I appreciate your question.

The size of implant best for you is dictated by your
chest wall measurements. Once we determine that we can choose the profile
based on what you want or need to achieve.  If you are seeking a natural look, then the diameter of the implant should be equal to or, more ideally, smaller than the width of your breast. The breast width is a measurement of how wide your breast is at the base, which should be measured at the level of the nipple. Choosing an implant that is smaller in diameter than your breast width will avoid the "side breast" fullness that is often associated with a more artificial appearance. Other than that, you should choose the implant based on volume, not on the dimensions of the implant. You should choose a board certified plastic surgeon that you trust to help guide you in this decision.

Silicone will give you a fullness at the
top (upper pole fullness).

Silicone implants come pre-filled with a
silicone gel and are the softest implant available. They feel more natural,
which makes them a good option for women with less natural breast tissue; but
they require a larger incision. It may be more difficult to realize if this
type of implant has ruptured, so it is important to monitor them with annual
follow-up visits. Additionally, because this implant contains a more liquid
silicone (less cross-linked), if this implant should rupture, it will leak only
into the scar capsule formed around the implant but may cause some discomfort
or implant distortion.

Anatomic gummy bear implants might be a
good choice to give you volume.

These highly-sought-after, anatomic
implants offer a look that more closely resembles the natural silhouette of a
breast, and, therefore, are a very attractive option for individuals seeking a
natural-looking, aesthetic primary breast augmentation. Additionally, these
implants are an especially excellent option for patients undergoing restorative
or corrective breast surgery because they provide more stability, shape, and
reduced incidence of capsular contracture. Compared to other types of silicone
gel implants, the silicone in the cohesive gel implant is more cross-linked;
therefore, should the implant shell “rupture,” it maintains its shape and
silicone does not leak.

During your breast augmentation
consultation, you should feel the different types of implants available, and
try on various implant sizers in front of a mirror to help you to get an idea
of how you will look following the surgery. You should also bring pictures of
the look you would like to achieve, as well as a favorite top to wear when
trying on implant sizers.

The best way to assess and give true
advice would be an in-person exam.

Please see a board-certified plastic
surgeon that specializes in aesthetic and restorative breast surgery.Best of luck!

Dr. Schwartz

Board
Certified Plastic Surgeon

Director-Beverly
Hills Breast and Body Institute

#RealSelf100Surgeon

Without  an exam, it is difficult to say what size implant would be right for you. Best to be seen in person.

Hello based upon your height and weight 400 cc implants are quite sizeable. Your breast and chest dimensions are the most important factors in determining your appearance. DrBurnett#realself100

Hi and thanks for the question.generally your plastic surgeon is the best to give such advice which is based on sizing with either breast implants in your bra or silicone chicken fillets to do the same thing.  Based on the information you have provided, 400cc is a large augmentation and will see you gop from a B-cup to at least a DD-E cup (assuming the surgeon can actually fit this implant in your breasts without causing a "Double Bubble".  It would be difficult to put these implants in someone of your size and maintain a natural appearance so i assume this is not something that is important to you.I hope that helps.Kind regardsDr Mark Hanikeri MBBS, FRACSPerth Specialist Plastic Surgeon

Thank you for the question.
As you can imagine, despite your good description of body type and goals, it is not possible to give you precise advice online. 
The best online advice I can give to ladies who are considering breast augmentation surgery 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're 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. I have found that the use of words such as “natural” or “C or D  cup” or "huge" 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.
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.I hope this (and the attached link) help.