Need help with passive intake size

Hey guys, im planning on finishing my first DIY box. The size is 2x2x4 and I'm running a 6" inline duct fan for my exhaust. Im having trouble finding out what size my passive intake size should be. Any help would be great. Oh and would it be necessary to put a carbon filter over the intake or would the negative pressure keep the smell from leaking.

I believe the rule is about twice the size of your 6 inch duct for passive. You should not need to filter the intake..as you say negative pressure should keep air or smell from leaking.

Awesome, thanks man

6" fan on that small of a box is pretty large.

Just leave some gaps around the door or drill a couple holes toward the bottom in your cab. 6" fan will suck out everything and more

Really? Its only a 160 cfm. Even with a carbon filter bogging it down its too much? Fml...

Use a small house ac filter on intake just to keep dust debri and bugs out. I would just use a 6 inch intake hole and get fan speed controller to dial in the fan to what works for you