How to use it
- Choose the Units and measure the room's Wall perimeter and Wall height.
- Enter the Ceiling length and Ceiling width, or 0 if the ceiling is not boarded, and add up the Area of doors and windows.
- Enter the Sheet width and Sheet length of the board you buy, and a Waste allowance.
- Read Sheets to order and Net area to board.
How the sheets are counted
The walls are the perimeter of the room times its height. The ceiling is its length times its width. The doors and windows are taken off the total, because they are not boarded.
The net area, with the waste added, is divided by the area of one sheet. The result is rounded up, because a part sheet has to be bought as a whole one.
walls = wall perimeter × wall height
ceiling = ceiling length × ceiling width
net area = walls + ceiling − openings
sheets to order = net area × (1 + waste) ÷ area of one sheet, rounded upWhat the count does not include
- Cuts. The count works on area only. A sheet cut to fit a corner or an opening can leave an offcut that is not used; the waste allowance covers this.
- More than one layer of board. Each layer needs its own count.
- Beads, tape, filler, screws and the frame the board is fixed to.
Worked example: a 4 m × 3 m room, 2.4 m walls, 2.5 m² of doors and windows, 1,200 × 2,400 mm sheets and 10 % waste
The walls are 14 × 2.4 = 33.60 m² and the ceiling is 4 × 3 = 12.00 m². Less 2.50 m² of openings, the net area is 43.10 m².
A sheet is 1.2 × 2.4 = 2.88 m². With 10 % waste, 43.10 × 1.1 = 47.41 m², and 47.41 ÷ 2.88 = 16.46, rounded up to 17 sheets.
| Result | |
|---|---|
| Net area to board | 43.10 m² |
| Area of one sheet | 2.88 m² |
| Sheets to order (10 % waste) | 17 |
Frequently asked questions
How do I work out the sheets for a room?
Multiply the wall perimeter by the wall height, add the ceiling length times its width, and take off the doors and windows. Divide that net area by the area of one sheet, add the waste, and round up.
Why are the sheets rounded up?
A sheet cannot be bought in part, so any fraction of a sheet becomes a whole one. The figure is the number of sheets to order, not the exact fraction of a sheet.
How much waste should I allow?
The waste allowance is your choice. Cut offs at corners, around openings and at the ends of walls are the main source of waste, so a room with many corners or small pieces needs more than a plain room.
Does the sheet size have to match the board I buy?
Yes. The count uses the sheet size you type, so read it from the data sheet of the board you choose, because the product decides the size.
Does the tool store what I enter?
No. The count runs in your browser, and nothing you type is sent to us or stored.
Sources
Figures and text last checked on Thursday, November 12, 2026.