The Drywall Calculator calculates how many sheets of drywall (sheetrock or plasterboard) you need by dividing the area to cover by the area of one sheet and adding waste.
Use the Walls mode for one or more walls with doors and windows (it also estimates screws), or the Room mode for all four walls plus the ceiling. Sheet size is adjustable — 4 × 8, 4 × 10, 4 × 12 ft or metric boards.
Drywall Calculator
Drywall (sheetrock / plasterboard) sheets and screws for walls or a whole room including the ceiling.
Formula
- Walls: Sheets = (L × H − openings) ÷ sheet area × (1 + waste %)
- Room: Area = 2(L + W) × H − openings + L × W (ceiling)
- Screws: sheets × screws per sheet
Where L = length, W = room width, H = wall height.
How the Calculation Works
Step 1: Calculate the area to cover and subtract doors and windows.
Step 2: Divide by the sheet size and add the waste allowance.
Step 3: Round up to whole sheets and multiply by your screw count per sheet.
Variables Explained
| Input | Meaning |
|---|---|
| Sheet width × length | Board size you’ll buy |
| Openings | Doors and windows not covered |
| Screws per sheet | Depends on framing spacing and whether it’s a wall or ceiling |
| Waste | Extra for cuts and breakage |
Example Calculation
One wall
Given: 20 × 8 ft wall, one 36 × 80 in door, one 36 × 48 in window, 4 × 8 sheets, 10% waste, 32 screws per sheet
Net area: 160 − 32 = 128 ft²
Sheets: 128 ÷ 32 × 1.1 = 4.4 → 5 sheets; screws: 160
Whole room with ceiling
Given: 14 × 12 ft room, 8 ft walls, 45 ft² of openings
Area: 2 × 26 × 8 − 45 + 168 = 539 ft²
Result: 539 ÷ 32 × 1.1 ≈ 18.5 → 19 sheets
Common Sheet Sizes
| Sheet | Area |
|---|---|
| 4 × 8 ft | 32 ft² |
| 4 × 10 ft | 40 ft² |
| 4 × 12 ft | 48 ft² |
| 1.2 × 2.4 m | 2.88 m² |
Material Estimation Notes
Longer sheets mean fewer joints to tape. Joint tape, compound, corner bead and screws depend on the layout; screw spacing is set by the manufacturer and local code, so enter the count that matches your installation.
Waste Factor Considerations
Rooms with many openings, angles or short walls create more offcuts. The right allowance depends on the room layout and sheet length.
Frequently Asked Questions
How many sheets of drywall do I need for a 12 × 12 room?
Walls: 4 × 12 × 8 = 384 ft² before openings, about 12 sheets of 4 × 8; add 144 ft² for the ceiling (about 5 more), plus waste.
How do you calculate drywall?
Area to cover ÷ sheet area, plus waste.
Should I subtract doors and windows?
Yes, for a closer estimate; small offcuts from openings are often waste anyway.
How many screws per sheet of drywall?
It depends on the framing spacing and the fastening pattern your code or manufacturer requires.
Is it better to use 4 × 8 or 4 × 12 sheets?
Longer sheets reduce joints but are heavier to handle. Enter either size to compare.