Yes - but that may not be in your best interest. In general, it's ABOUT 200 grams per bra cup size, but it's less than that when you're going from a AAA to a AA, and more if from a C to a D. It's also more if you're a larger person and less if smaller. With this procedure (breast reduction) there is a volume reduction but you have to maintain enough tissue to support (ie, allow adequate blood supply for) the nipple and areola and, at the same time, you want to have an aesthetic shape. Going too small could impair the blood supply and/or adversely impact the overall shape. I would, therefore, suggest that you discuss this with your plastic surgeon and take his or her advice rather than setting your sights on a specific bra cup size. And, finally, bra sizes vary widely from manufacturer to manufacturer; in the end, what's important is finding out what's appropriate for you, your frame and the look you'd like to achieve. And that's a critical part of your discussion with your plastic surgeon.
I hope that this helps, and good luck,