How to use the drywall calculator
- Enter the room length, width and wall height.
- Enter the number of doors and windows. A standard size for each is subtracted from the wall area.
- Choose your sheet size. Longer sheets mean fewer joints to tape on long walls.
- Tick “Include the ceiling” if you are boarding it, and keep a 10–15% waste allowance for offcuts.
The formula
Wall area = 2 × (length + width) × wall height − doors − windows Total area = wall area + ceiling area Sheets = total area × (1 + waste %) ÷ area of one sheet (rounded up)Worked example
A 12 × 12 ft room with 8 ft walls, ceiling included, no openings subtracted, 10% waste and 4 × 8 ft sheets:
- Walls: 2 × (12 + 12) × 8 = 384 sq ft. Ceiling: 12 × 12 = 144 sq ft. Total: 528 sq ft.
- With 10% waste: 580.8 sq ft.
- 580.8 ÷ 32 = 18.2, so you would buy 19 sheets.
Common sheet sizes
| US | Metric (plasterboard) |
|---|---|
| 4 × 8 ft = 32 sq ft | 1.2 × 2.4 m = 2.88 m² |
| 4 × 10 ft = 40 sq ft | 1.2 × 2.7 m = 3.24 m² |
| 4 × 12 ft = 48 sq ft | 1.2 × 3.0 m = 3.6 m² |
Tips
- Moisture-resistant board is commonly used in bathrooms and other damp areas.
- Screw spacing differs between walls and ceilings and between products. Follow the manufacturer's fastening schedule and your local building code.
- Plan sheet layout so joints do not line up with the edges of doors and windows, which helps reduce cracking.
Frequently asked questions
How many sheets of drywall do I need for a 12 × 12 room?
With 8 ft walls, the walls cover 384 sq ft and the ceiling 144 sq ft. Including the ceiling and 10% waste that is about 19 sheets of 4 × 8 ft drywall, or about 14 sheets for the walls alone.
Should I subtract doors and windows?
Subtracting them gives a tighter estimate, and the calculator does this using standard sizes. Some installers do not subtract small openings because the offcuts are rarely reusable; a 10–15% waste allowance covers this.
How many screws do I need per sheet?
A common rule of thumb is about one screw per square foot of board, so roughly 32 for a 4 × 8 ft sheet. The exact number depends on framing spacing and the fastening schedule you follow.
Which sheet size should I use?
Use sheets that match your wall height or that span long walls with fewer joints. Fewer joints mean less taping and finishing, but longer sheets are heavier to handle.