Passive intake please help

how big should my intake hole be if i have a 4inch rvk fan? 250 watt hps and a 5foot tall,3 foot wide and deep growing area?

check here https://www.greenpassion.org/index.php/topic/3401-what-size-vent-fan-do-i-need-and-intake-area-size/

or here http://lmgtfy.com/?q=calculating+passive+intake

i usually just use an intake hole slightly larger than the exhaust hole.

i run a stanley blower on high speed out a 6" exhaust. my passive intake is 7"

i seem to have plenty of air coming in and still have a slight negative pressure.

The stronger the negative pressure the better the circulation will be. High negative pressure pulls air in faster (in speed not volume) and hence will travel further.