How to use this drywall calculator
Enter the room's length, width and wall height, then count the doors and windows. Choose whether you're covering the ceiling and which sheet size you'll hang. Leave about 10% for waste; cuts around openings, outlets and corners always leave offcuts that are too small to use.
Along with the sheet count, the calculator estimates the other materials you'll need using common rules of thumb: about one screw per square foot of board, about 370 feet of joint tape per 1,000 ft², and about one gallon of ready-mixed joint compound per 100 ft² for taping and three coats.
The drywall formula
Sheets = ⌈ (wall area − openings + ceiling) × (1 + waste %) ÷ sheet area ⌉
A 4 × 8 sheet covers 32 ft², a 4 × 10 covers 40 ft² and a 4 × 12 covers 48 ft².
Worked example: a 14 × 12 ft room with 8 ft walls, one door, two windows and the ceiling included. The walls are 2 × (14 + 12) × 8 = 416 ft². Subtract 21 ft² for the door and 30 ft² for the windows to get 365 ft², then add the 168 ft² ceiling for 533 ft². With 10% waste that's 586 ft², and 586 ÷ 32 = 18.3, so you'd buy 19 sheets of 4 × 8.
Which drywall size and thickness?
| Use | Common choice |
|---|---|
| Interior walls | 1/2 in, 4 × 8 or 4 × 12 sheets |
| Ceilings | 1/2 in sag-resistant or 5/8 in |
| Garage walls shared with the house, furnace rooms | 5/8 in Type X (fire-rated), where code requires it |
| Bathrooms, laundry rooms | Moisture-resistant board; cement board behind tile in showers |
Longer sheets mean fewer joints to tape and a smoother finish, but a 4 × 12 sheet weighs around 70–80 lb and needs two people. If you're working alone or carrying sheets up stairs, 4 × 8 sheets are much easier to handle.
Tips for hanging drywall
- Hang the ceiling first, then the walls, so the wall sheets help support the ceiling edges.
- Run sheets horizontally on walls up to about 9 ft tall. You get fewer seams, and the seams sit at a comfortable height for taping.
- Stagger the end joints so they don't line up from one row to the next, which reduces cracking.
- Don't overdrive screws. The head should sit just below the surface without tearing the paper face.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
With 8 ft walls, the walls are 384 ft² and the ceiling is 144 ft². After subtracting a door and a window and adding 10% waste, you need about 540 ft², or 17 sheets of 4 × 8 drywall.
Should I subtract doors and windows when estimating drywall?
Subtract large openings such as doors, patio doors and big windows. Many installers don't subtract small windows, because the piece cut out is usually too small to reuse, so the waste allowance absorbs it.
How many screws per sheet of drywall?
About 28–32 screws for a 4 × 8 sheet on walls with studs 16 inches apart, and a few more on ceilings. A useful rule is roughly one screw per square foot of board.
How much joint compound do I need?
Plan on about one gallon of ready-mixed joint compound for every 100 ft² of drywall to tape and apply three finishing coats. A 4.5-gallon bucket finishes roughly 450 ft².
Results are estimates. Fire-rated and moisture-resistant board may be required by your local building code in some rooms.