How to use the drywall calculator
- Enter the room length, width and wall height, or switch to Wall area if you have already measured it.
- Tick Include the ceiling if you are boarding it too.
- Enter the number of doors and windows. Change their sizes if yours are not standard.
- Choose your sheet size and keep 10% extra for cuts.
Drywall formula
Wall area = 2 × (Length + Width) × Height Ceiling = Length × Width Net area = Walls + Ceiling − Doors − Windows Sheets = Net area × (1 + waste %) ÷ Sheet area → round up
Worked example
A 12 × 10 ft bedroom with 8 ft walls, one door and two windows, using 4 × 8 sheets:
- Walls = 2 × (12 + 10) × 8 = 352 ft²
- Openings = 21 + 2 × 15 = 51 ft² → net 301 ft²
- With 10% extra = 331.1 ft² ÷ 32 = 10.3 → 11 sheets
- Screws ≈ 300; tape ≈ 110 ft
Sheet sizes and coverage
| Sheet | Area | Typical use |
|---|---|---|
| 4 × 8 ft | 32 ft² | DIY, small rooms, 8 ft walls |
| 4 × 10 ft | 40 ft² | Taller walls, fewer butt joints |
| 4 × 12 ft | 48 ft² | Pros, hung horizontally |
| 54 in × 12 ft | 54 ft² | 9 ft walls with two rows |
| 1200 × 2400 mm | 2.88 m² | Standard metric plasterboard |
| 1200 × 2700 mm | 3.24 m² | 2.7 m ceilings |
For rooms with sloped ceilings or gable walls, work out each triangle as ½ × base × height, add it to the wall area and use the Wall area option.
Choosing the right board
- Thickness: 1/2 in (12.5 mm) is standard for walls. Use 5/8 in (15 mm) on ceilings with wide joist spacing and where fire-rated walls are required.
- Moisture-resistant board (green or purple) for bathrooms and laundries — and cement board behind shower tiles.
- Fire-rated (Type X) board is often required on garage walls shared with the house.
- Hang ceilings first, then walls, so the wall sheets support the ceiling edges.
- Stagger joints and avoid joints right at the corners of doors and windows, where cracks start.
The screw and tape numbers are estimates for standard framing at 16 in (400 mm) centres. If you are boarding a basement or garage, remember the stairwell walls and any soffits or bulkheads around ducts. Joint compound use varies more than anything else, depending on how many coats and how smooth a finish you want, so buy some extra and return unopened buckets.