How to calculate drywall
- Measure the room — length, width and wall height.
- Decide on the ceiling. Tick the box to include it; ceilings are often hung with longer sheets or ⅝ in board.
- Subtract openings. A standard door is about 21 sq ft and a typical window about 15 sq ft. Many installers don't subtract small windows because the cut-out is waste anyway.
- Add waste of 10–15% for cuts, and choose the sheet size you'll hang.
Drywall formula
Net area = Wall area + Ceiling − Openings
Sheets = Net area × (1 + waste) ÷ Sheet area
Worked example
A 12 × 12 ft room with 8 ft walls has 384 sq ft of wall and 144 sq ft of ceiling. Subtracting one door and two windows (51 sq ft) leaves 477 sq ft. With 10% waste that's 524.70 sq ft — 17 sheets of 4 × 8 or 11 sheets of 4 × 12.
Drywall sheets per room
8 ft walls, 10% waste, no openings subtracted:
| Room | Walls only (4×8) | Walls + ceiling (4×8) | Walls + ceiling (4×12) |
|---|---|---|---|
| 10 × 10 ft | 11 | 15 | 10 |
| 12 × 12 ft | 14 | 19 | 13 |
| 12 × 14 ft | 15 | 21 | 14 |
| 14 × 16 ft | 17 | 25 | 17 |
| 16 × 20 ft | 20 | 31 | 21 |
Choosing drywall
| Type | Typical use |
|---|---|
| ½ in standard | Most interior walls |
| ⅝ in Type X (fire-rated) | Garage walls shared with the house, ceilings below living space, where code requires |
| ½ in sag-resistant ceiling board | Ceilings with framing at 24 in spacing |
| Moisture/mold-resistant | Bathrooms (outside wet areas), laundry rooms, basements |
| Cement board | Behind tile in showers and tub surrounds |
Finishing materials (rules of thumb)
- Joint compound: about 1 gallon per 100 sq ft of board for a standard three-coat finish.
- Paper tape: about 370 ft per 1,000 sq ft.
- Screws: roughly 30–35 per 4 × 8 sheet on walls at 16 in framing; ceilings need more.
Larger sheets mean fewer seams to tape and finish, but they are heavier and harder to carry up stairs.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
With 8 ft walls, a 12 × 12 room has 384 sq ft of wall — 14 sheets of 4 × 8 with 10% waste. Including the 144 sq ft ceiling it needs about 19 sheets.
How many square feet is a sheet of drywall?
A 4 × 8 sheet is 32 sq ft, 4 × 10 is 40 sq ft, 4 × 12 is 48 sq ft and 4½ × 12 is 54 sq ft.
Should I subtract doors and windows?
Subtract doors and large openings. For small windows many installers hang over them and cut out afterwards, so the board isn't saved — keep a 10–15% waste allowance either way.
How much joint compound do I need?
Plan on about one gallon of ready-mixed compound per 100 sq ft of drywall, or roughly 10 gallons per 1,000 sq ft for three coats.
Is 4×12 drywall better than 4×8?
4 × 12 sheets cover long walls with fewer joints, which saves taping time. 4 × 8 sheets are lighter and easier to handle alone or in tight spaces.