40 to 45 cm2 should be more than enough but as i said if you have thich hair 40 is enough, with thin hair 45-50 is enough. You have to understand that most good doctors dont work like that. They are placing the grafts inder magnification and according to that they are placing grafts and calculate the density. Nobody says i will do 40 or 50. And of course you can always start with a first pass with lower density to increase the survival rate. After that you can always add and improve density. There are many options. But its not wise to go with density over 50 on the hairline, this might impact the survival rate.