What is the difference between the size of 300cc and 425cc gluteal implant?

To specifically answer your question - there is a 125 cc difference between the two implants you mentioned. To give you a visual of how much volume that is - about 4 shot glasses. Use a measuring cup and place that amount of water in a baggy to see how much volume that is.Please also note there are different shaped implants to consider

One of
the most important factors in creating the perfect derriere with implants is
indeed selecting the right size AND shape. I have found the best way to assure
this is to simply measure the actual dimensions of the patient’s buttock
cheeks. With these anatomical measurements, I can select an implant that not
only significantly augments the buttock but also supplies the correct
3-dimensional enhancement to look as real as possible. Therefore the only way
for you to know what implant works best is to consult with a board certified
plastic surgeon specializing in this procedure and have him/her take your
measurements before selecting an implant and proceeding with surgery.

The largest buttock implant currently available in the USA is a 690cc round
implant. Indeed custom implants can be ordered larger, not only at a premium
price but at a premium risk for most patients'. Unlike breast implants which
are placed under the very expandable tissue of the breast and half of the
pectoral major muscle, buttock implants are (most preferably) placed under (or
at least within) the largest strongest muscle of the body, the gluteus maximus
muscle, which is not nearly as expandable or forgiving. Thus most patients
simply do not have a large enough native buttock muscle to fit an implant over
even 500 ccs', without leading to significant complication such as wound
breakdown/opening &/or implant exposure...necessitating removal.

Thus some of those sought after video-vixen and celeb-types (without mentioning
names) with cartoonish bottoms could have either gotten extremely lucky
with a huge oversized implant, had a very large volume of filler
injected such as silicone or hydrogel (all highly NOT recommended because of
possible risk of severe infections and even deadly complications),
and/or have been genetically "blessed".

I generally do not recommend fat grafting at the same time as placing buttock
implants because of a significantly increased risk of infection. For fat to
survive it must be grafted into muscle, however that is also where the implant
sits. Thus, if fat it injected into the implant or implant pocket then it will
die and almost assuredly get infected - necessitating removal of the implant as
well.

Nonetheless, buttock implants are a proven safe and effective method of buttock
augmentation as long as the recommendations of a board certified plastic
surgeon specialist are adhered to.

Glad to help.

Hard to advise you on this without seeing you and measuring you to determine what may be more appropriate.Kenneth Hughes, MDLos Angeles, CA