Attic Ventilation rule...

Area of ceiling adjacent to the attic divided by 300 for a home less than 20
years old.
(divide by 150 for older homes)

Take resulting square ft and divide by 2

This will give you the required square feet of upper and matched reqired
ventilation are for lower ventilation.

Example: 2000 sq ft of ceiling / 300 = 6.7

6.7 / 2 = 3.3

The example home needs 3.3 square ft (480 sq inches) of upper ventilation
and the same for lower ventilation.

TAB Dude