It appears that you are opting for implant-based reconstruction of your breasts, for which I wish you the best during your mastectomy and reconstruction...excellent results can be achieved with such.This is a very common question asked during breast reconstruction. The volume needed to achieve this result will differ amongst each woman. You must take into account body habitus, height, weight, as well as the projection-type of implant used. A smaller woman will require much less volume (cc's) than a much larger and taller woman would. The chest girth in inches (36, 38, etc.) will not change as this is a measure of the chest circumference beneath the breasts. The cup size (B, C, D, etc.) is measured by the projection from the chest. Also, this is always variable, as not all bras are made standard and one brand may give a different cup size from another. Determining this value during your expansion process, if you are having tissue expanders placed initially, may be the easiest way, as you could see the size as it expands and determine for yourself when you are happy with the size in clothing. Your surgeon would then put in a similar volume upon the exchange of your expanders for the implants.