Bra size is not a standardized measurement. It is much like dress size. How can you define what “size 2″ means in dress sizes. In the same way cup size varies between different brands and is only really useful as a relative comparison between the same brand and chest diameter, though still not possible to predict accurately. It is best to wait at least 6 weeks at which point a majority of the swelling should be resolved and the implant should be at a stable position.