Surgical hair restoration produces an illusion of coverage. Generally speaking, the average patient with average hair characteristics can achieve a great look of restoration at 50% of original density. Obviously there are some diiferences patient-to-patient.
Your next question has to do with yield. That will vary doctor-to-doctor. MAKE SURE and VERIFY your surgeon employs microscopic dissection of the grafts to avoid transection as much as possible. With a talented competent proven hair transplant surgeon and surgical staff, the yield can be as high as 90%. Just know that there is no such thing as 100% yield. Any deficiency of blood supply in the recipient area, scar matter developed from previous surgeries, and simply the variance in how patients heal because of their biological differences also can have a bearing on the overall yield.