How much window area do I need for natural light and ventilation in a room?

Glazing must be at least 8% of floor area for light, and openable area at least 4% for ventilation (IRC R303.1).

Habitable rooms must have an aggregate glazing (glass) area of not less than 8 percent of the room's floor area to provide natural light.

For natural ventilation, the minimum openable area to the outdoors must be at least 4 percent of the floor area being ventilated, through windows, doors, louvers, or other approved openings.

These window requirements can be waived where approved artificial light and a mechanical ventilation system are provided instead, as set out in the exceptions to this section.