Measuring a room for plasterboard
Walls first: the perimeter of the room times the wall height, less doors and windows. Then the ceiling, which is simply length times width. Add the two, add waste, and divide by the area of the sheet you intend to use. That is the count. The calculator does walls and ceiling separately so you can see where the sheets are going and order different lengths for each if it helps.
sheets = (net area × (1 + waste)) ÷ sheet area, rounded up
Choosing a sheet size
Australian plasterboard is 1200 mm wide and comes in lengths from 2400 to 6000 mm. On walls, sheets are usually fixed horizontally, so a 2.4 m wall takes two sheets high and the length you want is the one that spans the wall with the fewest butt joints. A 3.5 m wall in 3600 sheets has no joins; the same wall in 2400 sheets has a join in every course and an offcut. On ceilings, longer sheets mean fewer joints to set, which is where the labour goes, but 4800 and 6000 sheets need two people and a clear path in. Ten millimetre board is standard for walls and for ceilings on battens at 450 mm centres; 13 mm goes on ceilings framed at 600 mm and on fire and acoustic walls.
| Sheet | Area | Suits |
|---|---|---|
| 2400 × 1200 | 2.88 m² | Small rooms, one person, tight access |
| 3000 × 1200 | 3.60 m² | Walls up to 3 m without a join |
| 3600 × 1200 | 4.32 m² | Most bedroom walls |
| 4200 × 1200 | 5.04 m² | Living room walls and ceilings |
| 4800 and 6000 × 1200 | 5.76 and 7.2 m² | Long ceilings, two people |
Fixing
Walls are fixed with daubs of stud adhesive on every stud and screws around the perimeter of the sheet at about 300 mm centres, which comes to roughly 15 screws and a third of a cartridge per 2400 × 1200 sheet. Ceilings are screwed only, into every batten at 300 mm centres across the sheet, so about double the screws. Use 25 mm needle-point screws for 10 mm board on timber, 32 mm for 13 mm board, and fine-thread screws on steel framing. Adhesive must not go near the joints or it will crack the set.
Setting and cornice
Joints get paper tape bedded in a base coat, a second coat feathered wider, and a top coat sanded smooth: three coats, and about 1.2 kg of compound per square metre of board across the three. Screw heads are filled with the same coats. Cornice runs around the perimeter of the ceiling, fixed with cornice cement mixed on the spot, at roughly a bag per 25 lineal metres of 90 mm cove. Square-set ceilings skip the cornice but need metal angles and more setting time at the wall-ceiling junction.
Worked example
A bedroom 4 × 3.5 m with a 2.4 m ceiling, one door and one window totalling 4 m². Walls: 15 m of perimeter × 2.4 = 36 m², less 4 m², is 32 m². Ceiling 14 m². In 2400 × 1200 sheets with 12 percent waste that is 13 wall sheets and 6 ceiling sheets, 19 in all. Screws about 330, adhesive 16 cartridges, tape 56 m, compound 56 kg, cornice 16 m and one bag of cornice cement.
Common questions
What sizes does plasterboard come in?
1200 mm wide, in 2400, 2700, 3000, 3600, 4200, 4800 and 6000 mm lengths, 10 or 13 mm thick.
How many sheets for a room?
Wall area less openings, plus ceiling, plus 10 to 15 percent, divided by the sheet area. A 4 × 3.5 m room is about 19 sheets of 2400 × 1200.
How many screws per sheet?
About 15 per 2400 × 1200 sheet on glued walls, about 30 on ceilings.
How much compound?
About 1.2 kg per m² over three coats, so a 20 kg bag of base coat does about 17 m².
Quantities only. Board type, thickness, fixing centres and wet area requirements follow AS 2589 and the board manufacturer's installation guide.