Anyone who is considering breast augmentation surgery and has done even just a little research knows that implants comes in volumes, not cup sizes. An appropriate size implant needs to be selected by the patient and their surgeon to obtain the desired increase in size.
Cup Size Change Only
The purpose of a breast augmentation is to increase the cup size only. Many patient believe that the number (e.g. 32, 34, 36, etc.) changes with the breast augmentation surgery but that is not correct. The number on the bra size has to do with the measurement of chest size only and has nothing to do with the actual breast size or volume.
Bra manufacturers have designed this measurement so that is relates to chest size but is not, in face, the actual measurement. If the number, in inches, around a women's chest below her breasts is an odd number, you add 5 inches to get the bra size; if it is an even number, you add 4 inches. So two women with different measurements, one 27 inches and one 28 inches would both be put into a 32 inch bra. This is why most bras are only manufactured in even sizes.
The cup size of the bra is related to the volume of the breast and is the only thing that changes with breast augmentation surgery. There is no exact way to measure for cup size and there is certainly no uniformity among bra manufacturers with respect to cup size measurement. More than one bra manufacturer (and one in Columbus, Ohio), which feature a lot of push-up bras tends to markedly exaggerate bra cup sizes. It is no wonder that many women have no idea what their cup size it.
One thing that is consistent is that the difference between cup sizes for a larger bra size like a 36 is larger than the difference between cup sizes for a smaller bra like a 32. Therefore, patients with larger chest measurements who want to go up two cup sizes need considerable larger breast implants than those with smaller chest sizes who also want to go up two cup sizes.
When all is said and done, the implants have 'settled' and the skin has expanded and relaxed, the end result in size is not an addition of the volumes of the implant and the breast prior to surgery. Tissues in the body respond to the stresses applied to them, which is why women wind up with loose, excess skin on their abdomens after pregnancy and muscles, bones, and tendons get larger with vigorous exercise. The pressure from the implant results in compression of breast tissue and any fat in the breast; a process known as atrophy. The degree to which this occurs is difficult to determine and tends to happen more with larger implants. In addition to swelling going down, this is another reason why the breasts decrease a little in size in the first few months after surgery.