How many grafts can be taken from the donor area by FUE safely without over-harvesting

The donor area in the average Caucasian male has ~12,500 Follicular Units of which possibly up to 60% can be taken for hair transplants. For FUE without becoming over-harvested, about half of this amount (30% or 3,750 grafts) can be taken with FUE to be safe. The thickness of the hair shaft (fine, medium or coarse) alter this number (lowers if for fine hair and increases it for coarse hair). The question to ask, is how much hair do I have to leave behind to keep my donor area LOOKING healthy and full enough not to reveal that I was transplanted.