HOW TO FIGURE HOW MUCH CFM I NEED

[Saturnalia]

So 6X6X7.5 = 270 Cubic feet. This is the volume of the space.
A 270CFM fan will change this entire space in 1 minute.
Ideally you need to change the entire air space in around 5 mins or less. So you can divide the space by 5 to give you your minimum size.
270/5 = 54 - this is the minimum size of fan that would do your space.
So your 270CFM fan is more than big enough for your space,

[Tomwolves]

Hello All, I am trying to figure out of big of intake fan and exhaust fan I need for my grow room build, which is 6x6x7.5 FT I would like to use a 4" inline fan for fresh air, and a 6" diameter for my exhaust. With my calculations I come up with a 270 CFM . Someone told me I need 800 cfm. So if anyone has the formula to figure it out I would appreciate tremendously. Thank you all, and have a awesome day!!