How the drywall calculator works
It adds up the area of the four walls (perimeter × height), adds the ceiling if you tick it, and takes off the area of doors and windows. Then it adds the waste percentage and divides by the area of one sheet, rounding up. A standard door opening is about 20 square feet and a typical window 12 to 15 square feet.
Which sheet size to use
4 × 8 sheets are the easiest to carry and fit through doors. Longer 4 × 10 and 4 × 12 sheets cover more area with fewer joints to tape, which saves finishing time, but they are heavy and usually need two people. For ceilings, longer sheets mean fewer joints overhead.
Thickness
Half-inch drywall is the usual choice for walls in homes. Five-eighths inch is used where fire-rated board is required, such as many garage walls next to living space, and is common on ceilings because it sags less between joists. Check your local code for fire-rated areas.
Frequently asked questions
How many sheets of drywall for a 12 × 12 room?
With 8 ft walls and the ceiling, the area is 528 square feet: 17 sheets of 4 × 8 before waste, or 19 with 10 percent extra.
How much waste should I allow for drywall?
About 10 percent for a simple room, 15 percent for rooms with many openings, corners or angled walls.
Should I subtract doors and windows?
Subtract large openings like doors and big windows. Many installers ignore small windows, because the offcuts are rarely reusable.