Vent help?

New guy and don’t know much but im giving this a shot.
Well I have built an indoor grow room, its 8'x9' and 8' high, I am using a 600wt hps light with reflector shade. I plan on running a ventilation system I the room.duh! I will be using 7" duct for both fresh air and exhaust. My main question is what size fan would work best fore this room? I guessing there is some sort of way to figure this out, but im not sure

Any help would be excellent!

well it usually goes 4" 6" 8" 10", a 6" extractor with 4" intake would be v good but in all honesty you would be better off getting a bigger fan putting a speed controller on it and running it at a lower speed (much quieter and more efficent) in that space i would go for the 8"
good luck m8
any other questions just ask
ripz