Should I get 150cc or 200cc to get a B cup?

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins").
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.
With regards to your particular question, I would not stress over small differentials in volume. 50 ml is slightly greater than the volume of a shot glass. If 200 ml is too large it is very likely that 150 ml would have felt large as well. Most patients will need a volume differential of 100 ml + in order to truly appreciate a volume difference. I will typically order sizes flanking a patient's chosen volume to allow for a day of procedure change of plans.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

After I measure and discuss goals with my patients, we then look at pictures of women (my patients) with similar measurements with different size and style breast implants. They also get to see what they would look like when the breasts have fully dropped and fluffed and in clothes. You get to see actual results and the surgeon's experience and not a virtual idea of what can be achieved. Women tell me that this process is very helpful in determining what size and style breast implant is right for them. Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author. RealSelf Distinguished Hall of Fame Inductee. Philadelphia, Pa., USA

Hello, it is common to feel nervous with size choice prior to surgery. Generally, 200cc is going to increase your breasts about a cub size. The difference between the two sizes is about the volume of a shot glass. Always remember to consider that our bodies are all different and the implants are not going to look the exact same on you as someone else.

-Dr. Joe