How to use this calculator
- Enter the room length, width and wall height in feet.
- Enter the number of doors and windows. Each is subtracted from the wall area.
- Choose whether to include the ceiling.
- Pick the sheet size you plan to buy. Longer sheets mean fewer joints but are harder to carry.
- Keep 10% for waste unless the room has many corners and cutouts.
How the numbers are calculated
Wall area is the room perimeter multiplied by the wall height. Each door is counted as 21 square feet (3 ft by 7 ft) and each window as 15 square feet (3 ft by 5 ft) and subtracted. If you include the ceiling, length times width is added.
The waste percentage is added and the total is divided by the area of one sheet, then rounded up. Screws are estimated at about one per square foot of board, tape at about 0.37 ft per square foot, and joint compound at about one 4.5 gallon bucket per 450 square feet. These last three are rules of thumb, not exact figures.
Worked example
A room 12 ft by 14 ft with 8 ft walls has 416 sq ft of wall. One door and two windows remove 51 sq ft, leaving 365 sq ft. With 10% extra you need 401.5 sq ft, which is 13 sheets of 4×8. That is about 420 screws, 136 ft of tape and 1 bucket of joint compound.
Tips before you buy
- Half-inch board is the usual choice for walls. Five-eighths inch is often used on ceilings to help resist sagging.
- Use moisture-resistant board in bathrooms and laundry rooms.
- Hang the ceiling first, then the walls, so wall sheets support the ceiling edges.
- Many installers do not subtract small openings, because cutting around them wastes board anyway. The 10% allowance covers this.
- Buy a little extra tape and compound. Finishing takes several coats and sanding.
Frequently asked questions
How many sheets of drywall do I need for a 12 by 12 room?
With 8 ft walls, one door and one window, and 10% waste, a 12 by 12 room needs about 12 sheets of 4×8 for the walls and about 17 sheets if you also cover the ceiling.
Should I subtract windows and doors?
You can, and this calculator does. Some professionals skip small openings because the offcuts are rarely reusable. The waste allowance gives you a safety margin either way.
How many screws are in a sheet of drywall?
Roughly 30 screws for a 4×8 sheet when spaced about 12 inches apart on walls and closer on edges. The calculator uses about one per square foot.
Are 4×12 sheets better than 4×8?
Longer sheets leave fewer seams to finish, which saves time. They are heavier and harder to move, so they suit larger rooms and ceilings if you have help.
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These results are estimates for planning purposes. Material sizes, densities and local requirements vary, so confirm quantities with your supplier or a qualified contractor before ordering.
Last updated October 11, 2026.