Volume for volume they are the same, but shape may be different depending upon the profile used. If you are looking of the approximate same shape then you should review the profile of the implants you have now and match them up with the silicone.
Good question. The size is the same regardless of whether your implant is saline or silicone. If you like the size of your breasts currently you can get an equivalent size silicone implant. If you need changes in projection or the width of your implant this can be accomplished by selecting a silicone implant with the proportions that meet your needs. If you increase either projection or width, the implant size will also be increased automatically.Good luck with your breast implant exchange.Dr Remus Repta