How many hair grafts would I need to lower my hairline? (Photos)

I was wondering if anyone could advise. I have a massive forehead, more of a 5/6 head rather than a “4” head. I’ve always been conscious of it since a child. I have extremely thick hair! I always get hairdressers commenting on its thickness and how they’ve not had a client with hair as thick, so I know I have plenty to spare. My aim is to lower my forehead with a hair transplant, as I don’t want the scars from foreheadplasty. How many grafts would I need to lower it?