Find the wall area and number of 4x8 sheets needed for your project.
Standard door and window openings are estimated at 21 and 15 sq ft respectively. Add about 10% extra material to cover cuts, waste, and mistakes.
It divides your total wall/ceiling square footage by the area of a single standard sheet (commonly 32 sq ft for a 4x8 sheet), then adds a waste allowance for cuts around doors and windows.
4x8 feet (32 sq ft) and 4x12 feet (48 sq ft) are the most common sizes sold at hardware stores.
A basic area calculation includes them unless you subtract their area separately — subtracting large openings gives a more materially accurate sheet count.