I recently had a breast revision from 300cc to 500cc. What size bra should I be? I don't feel as big as I should be. 4 days out.

A 500 cc implant is a very significant implant. Of course 500 cc will look bigger in a woman with a 34 chest than a 38 chest, and we do not know your measurements. Going from 300 cc to 500 cc means you increased the size of the implant by roughly 66 percent. Review your outcome with your doctor and let him/her know your concerns. Very large implants have negative consequences later in life, so keep that in mind when reviewing your goals. 

Going up 200 cc's in general can bump you up a cup or slightly more.  The best thing to do is to wait a 6-8 weeks before going for a fitting.

There really isn't an answer to this question. It depends on how much breast tissue you had to start with and then there is the fact that all bras size a bit differently.

There is no accurate/direct correlation between breast implant volume utilized and resulting cup size; in my opinion, “the 200 cc of a breast implant change equates to a cup size” statement simply does not hold true in many cases. Cup sizes are simply too variable;  discussing goals and/or outcomes of  breast augmentation surgery in terms of achieving specific cup sizes is really not helpful.It is not unusual for patients to have your concerns after breast surgery early after surgery; at this point, time and patience will be your best friends. Continue to follow-up with your plastic surgeon who will always be your best resource for information and/or reassurance.  Best wishes: hopefully, you will be please with the long-term outcome of the procedure performed ( best evaluated 6 months down the line).