Dear Ms. MomReady4myoldbody,Thank you for your story and questions .Unfortunately without a examination I can advise you in general terms, however I hope you will find them helpful.The amount of fat injected depends on:1) the amount of fat harvested2) the amount of suitable fat that is abel to be purified3) the "stretchability" of your buttock skin. One can try to gain weight prior to the procedure in hope that the areas you gain weight can be liposuctioned. Caveat: not all weight gain can not be harvested (some may be deposited on your internal organs or areas that can't be liposuctioned).Please make several appointments with experienced Plastic Surgeons who listens to your specific desires and who are not only Certified by the American Board of Plastic Surgery but in addition ideally a member of the American Society for Aesthetic Plastic Surgery (denoting by membership as having met additional criteria and a focus on Cosmetic Plastic Surgery).My best wishes, Dr. R. A. Hardesty, MD, FACSDiplomate and Certified by the Am. Bd. of Plastic Surgerywwwimagineplasticsurgery.com4646 Brockton AveRiverside, Ca 92506(951) 686-7600SHOW LESS