How much do my Sientra silicone gel 505 cc implants weight?

Sientra silicone gel breast implants weigh 1 gram per 1 cc which would be 1010 grams or 1 kilogram or 2.3 lbs. Weight gain after surgery is initially from water retention, but over the first month likely related to decreased activity from the recovery process. In general, this is improved as your self-confidence is bolstered and you feel better.

A 450 cc implant weighs one pound.  So you have a combined weight of a little over 2 pounds added to your body.  You are still healing and maybe you are retaining some water weight, also.  Best wishes!