Worked example: a 4 m × 3 m room
Four walls 2.4 m high, the ceiling boarded, in 2,400 × 1,200 mm boards with the calculator's 10% waste allowance.
| Stage | Figure | Working |
|---|---|---|
| Wall run | 14 m | The four walls around a 4 m × 3 m room |
| Walls | 33.6 m² | 14 m of run at 2.4 m high |
| Ceiling | 12 m² | 4 m × 3 m, if it is being boarded |
| Boarded area | 45.6 m² | Walls plus ceiling |
| With 10% waste | 50.16 m² | Offcuts at openings and the last board in each run |
| Sheets to buy | 18 | At 2.88 m² a 2,400 × 1,200 mm board |
Do not forget the ceiling
The ceiling is easy to leave out and it is a big part of the order: 12 m² of the 45.6 m² total. Board it in the same pass if you are doing it at all, because the sheet discount and the delivery are the same either way.
Why the waste allowance is doing real work
Sheets come in fixed 2,400 × 1,200 mm sizes, so the last board in every run is a cut. The 10% allowance covers those offcuts and the cuts around openings, and turns the bare room area into the order: at 2.88 m² a board, 50.16 m² is 18 sheets. A room with many windows and doors wastes more; a plain wall wastes less.
Screws, tape and the fixing method
Screws run at about 30 per m², which is 1,368 for this room — 2 boxes of 1,000. The joints and corners take about 69 m of scrim tape, so 1 roll of the common 90 m size. Whether you also need adhesive, corner bead or joint filler depends on the method: dot-and-dab onto masonry is a different job from screwing to studs.
How the calculator works
- Enter the room length, width and wall height.
- The wall run and ceiling area give the total area to board.
- The waste allowance is added, then the board size divides into it.
- Sheets round up, because a board is bought whole.
- Screws and tape follow the boarded area at their own rates per m².
Where to go next
Plasterboard FAQs
How many plasterboard sheets do I need for a 4 m × 3 m room?
18 sheets of 2,400 × 1,200 mm board. The four walls are 33.6 m² and the ceiling is another 12 m², so 45.6 m² becomes 50.16 m² once the 10% waste allowance is added.
Do I count the ceiling in the plasterboard order?
Only if you are boarding it — but if you are, count it: on this room the ceiling is 12 m² of the 45.6 m² total.
How many screws for plasterboarding?
About 30 per m² of board. For this room that is 1,368 screws, which is 2 boxes of 1,000.
How much scrim tape do I need?
The joints and corners here take about 69 m, so 1 roll of the usual 90 m roll.
What thickness of plasterboard should I use?
12.5 mm is the standard for walls and ceilings. A bathroom, a fire-rated wall or a room needing extra sound insulation may want a different board — check the specification before ordering.
Guidance only. The quantities above are planning estimates from the ProjectCalc calculators, not a quote and not a specification. Check your own measurements and your supplier's current product data before ordering.