Quick answer
Divide the area to board (walls plus ceiling, less doors and windows) by the area of one sheet and add about 10% for cutting. A standard 2400 × 1200 mm sheet covers 2.88 m², so a 4.2 × 3.6 m room with a 2.4 m ceiling, one door and one window needs 19 sheets including the ceiling.
The method
- Wall area = perimeter × ceiling height.
- Take off openings: about 1.5 m² per door and 1.44 m² per window (use real sizes if you have them).
- Add the ceiling if you're boarding it: length × width.
- Add 10% for cuts and offcuts, then divide by the sheet area and round up.
| Sheet | Size | Covers |
|---|
| Standard | 2400 × 1200 mm | 2.88 m² |
| Long | 3000 × 1200 mm | 3.60 m² |
| Small (easier to handle) | 1800 × 900 mm | 1.62 m² |
Worked example
| Step | Working | Result |
|---|
| Perimeter | 2 × (4.2 + 3.6) | 15.6 m |
| Walls, gross | 15.6 × 2.4 | 37.44 m² |
| Less 1 door and 1 window | 37.44 − 1.5 − 1.44 | 34.50 m² |
| Ceiling | 4.2 × 3.6 | 15.12 m² |
| Total with 10% waste | 49.62 × 1.1 | 54.58 m² |
| Standard sheets | 54.58 ÷ 2.88 | 19 sheets |
The same room needs about 1,068 drywall screws (around 20 per m² on walls and 25 per m² on ceilings, as the fixings are closer together overhead) and one 25 kg bag of jointing compound at roughly 0.5 kg per m².
Which board where
- Standard wallboard for most walls and ceilings.
- Moisture-resistant board (usually green) in bathrooms and kitchens, behind tiling.
- Fire-resistant board (usually pink) where Approved Document B asks for fire separation, such as garage ceilings and some escape routes.
- Acoustic board for party walls and floors to meet Approved Document E.
- 12.5 mm is standard on walls and on ceilings with joists at up to 600 mm centres; 9.5 mm is only for joists at 450 mm or closer.
