Enter the room dimensions, choose a sheet size and waste allowance, and get wall area, ceiling area and the number of drywall sheets needed.
Wall area is the room perimeter multiplied by the ceiling height, and ceiling area is length multiplied by width. Total area divided by the sheet area (32, 40 or 48 sq ft for 4x8, 4x10 and 4x12 sheets), increased by the waste allowance and rounded up, gives the sheet count. Door and window openings are not subtracted, which is deliberate for an estimate: the offcuts around openings are rarely fully reusable, and the waste allowance covers breakage, miscuts and damaged corners. Longer sheets reduce the number of joints to tape and finish, which is why 4x12 sheets are popular on long walls and ceilings despite being heavier to handle.
How many drywall sheets does a room need? Add the wall area (perimeter times ceiling height) and the ceiling area if it is being boarded, then divide by the sheet area and round up with a waste allowance. A 12 by 10 ft room with 8 ft ceilings and the ceiling included is about 472 sq ft, or roughly 17 sheets of 4x8 with 10% waste.
Should door and window openings be subtracted? For a sheet estimate, usually not. Openings are cut out of sheets anyway and the removed pieces are seldom fully usable elsewhere, so leaving the area in acts as part of the waste allowance and keeps the estimate safe.
Does sheet size change how many sheets are needed? The total area is the same, but larger sheets mean fewer, bigger pieces: 48 sq ft sheets cover the area in two-thirds as many pieces as 32 sq ft sheets, with fewer joints to finish, at the cost of heavier sheets that are harder to move through a finished house.