How much attic ventilation does Air Vent recommend for a typical attic? How do I calculate proper attic ventilation?

Research has shown that the best way to ventilate an attic is with a system that provides continuous airflow along the entire underside of the roof sheathing.

Research has shown that the best way to ventilate an attic is with a system that provides continuous airflow along the entire underside of the roof sheathing. Achieving this desired airflow requires a balanced system of intake ventilation low at the roof's edge or in the soffit/eaves and exhaust ventilation at the ridge. For optimum attic ventilation for today's tighter built, tighter remodeled homes that have more efficient building materials, Air Vent recommends 1 square foot of ventilation for every 150 square feet of attic floor space with half the ventilation represented by intake vents and half by exhaust vents such as ridge vents. Some absolute minimum building code requirements use the 1/300 ratio instead of the 1/150 ratio. Here's an example using the 1/150 ratio: 1. Square feet of attic space (defined as length x width floor of the attic) divided by 150 = square feet of net free area needed in total for the entire attic. 2. Total square feet of the net free area needed x 144 (which converts square feet into square inches) divided by 18 (which is the amount of net free area most ridge vents provide per linear foot) = linear feet of ridge vent needed for exhaust (for example, ShingleVent II). 3. Total square feet of the net free area needed x 144 (which converts square feet into square inches) divided by 9 (which is the amount of net free area many continuous intake vents provide per linear foot) = linear feet of continuous intake vent needed (for example, The Edge Vent). 4. To meet absolute bare minimum code requirements divide by 300 instead of 150 in Step 1.