How this calculator works
Wall area is the room perimeter × wall height; the ceiling is length × width. Standard door and window areas are subtracted, a waste allowance is added and the total is divided by the sheet area and rounded up.
Walls = 2 × (Length + Width) × Height
Ceiling = Length × Width (optional)
Net = Walls + Ceiling − Doors×21 − Windows×15
Sheets = round up( Net × (1 + Waste%/100) ÷ Sheet area )
Assumptions and tips
- Longer sheets mean fewer butt joints but are heavier to handle.
- Small openings are often hung over and cut out, so some pros skip the window deduction entirely.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Room length | 12 ft |
| Room width | 12 ft |
| Wall height | 8 ft |
| Include ceiling? | Yes |
| Doors | 1 |
| Windows | 2 |
| Sheet size | 4 × 8 ft |
| Waste allowance | 10 % |
| Result | Value |
|---|---|
| Drywall sheets | 17 sheets |
| Area to cover | 477 sq ft |
| Drywall screws (≈1 per sq ft) | 544 screws |
| Joint tape (≈370 ft per 1,000 sq ft) | 202 ft |
| Ready-mix joint compound (≈140 lb per 1,000 sq ft) | 77 lb |
Step by step:
- Walls = 2 × (12 + 12) × 8 = 384 sq ft
- Ceiling = 144 sq ft; openings = 51 sq ft
- Net = 477 sq ft; + 10% = 524.7
- Sheets = 524.7 ÷ 32 → 17
Drywall sheets for common rooms
8 ft walls plus ceiling, one door, one window, 10% waste.
| Room | 4×8 sheets |
|---|---|
| 10 × 10 ft | 14 sheets |
| 12 × 12 ft | 17 sheets |
| 12 × 16 ft | 21 sheets |
| 14 × 20 ft | 28 sheets |
| 20 × 20 ft garage | 35 sheets |
Common mistakes to avoid
- Using ½ in wallboard on ceilings with 24 in framing — ceilings often need sag-resistant board.
- Buying exact sheets with no spare for cuts around outlets and corners.
Frequently asked questions
How many sheets of drywall for a 12×12 room?
With 8 ft walls, a ceiling, one door and two windows, about 17 sheets of 4×8 including 10% waste.
Should I use 4×8 or 4×12 sheets?
4×12 sheets leave fewer seams to tape on long walls, but 4×8 sheets are easier for one person to carry and lift.