How to calculate light and air requirements?

1) Measure the room's floor area.

Calculate the total square footage of the room. For example, if a living room is 14 feet by 15 feet, the room's floor area is 210 square feet.

2) Calculate the required window size.

Multiply the room's floor area by 0.10 (10%) to find the minimum window area required for adequate light. In the example already mentioned, the room requires at least 21 square feet of window space.

3) Ensure proper ventilation.

Check that the room meets ventilation standards by ensuring that at least 5% of the floor area is dedicated to window that open for fresh air. Using the same example, 5% of 210 square feet is 10.5. Therefore, the room needs a minimum of 10.5 square feet of openable window space. 

New York Department of Building (NYC DOB)