Do Silicone and Saline Implants Weigh the Same?

This is a really insightful question. I gave a paper at our past National Aesthetic Society (ASAPS) on this topic specifically: "Differences between Silicone and Saline Implants Plastic Surgeons Need to Know"
Saline implant shell have weight and contribute up to 15-25 grams or cc's depending on the size of the implant. This is important because saline implants are filled in surgery and come empty. Silicone implants come pre-filled and actually their weight includes their shell, so as an example, if we are exchanging a patient's saline implants that were 300cc implants filled to 330cc's the implant actually weighs 350 cc's or ~350 grams. So if we are replacing a 330cc saline implant and put a 330 cc silicone gel implant in, it is actually 20cc's smaller. Also, the gel implants have less projection so will be slightly and look slightly smaller.
Next, Saline is actually more dense and weighs more than silicone gel. It is not a lot, ~.990 grams (gel) vs 1.02 grams (saline), but even 0.1 gram difference with a 500 gram implant is 50 grams or up to 50cc's different.
You need to recognize however that 30 cc's is only 2 tablespoons and it takes about 100 cc's difference for you to visualize a difference inside the body. But the answer is yes, there is a difference. The patient and the plastic surgeon need to know and discuss these differences. They are subtle, but measurable.

The difference is really not significant. So the weight that you have is roughly 2.2 lbs each.
You can reduce the size of the implants and the largest silicone implants that are available are 800 cc. Just remember that you may need some kind of a lift if you do go significantly smaller.
Good luck.

 The difference in weight between silicone and saline implants is negligible.  You really should not worry about the difference in weight for surgical decision making.  You should consider the volume and shape.  Good luck.