Plasterboard calculator
Count the sheets of plasterboard for walls and ceilings, less doors and windows, plus the jointing compound to tape and joint them.
Floor to ceiling.
Sheets to buy
- Sheets to buy
- 191200 × 2400 mm sheets: 13 for walls, 6 for the ceiling
- Area to cover
- 46.76 m²Walls 32.76 m², ceiling 14 m², after taking off 3.24 m² of doors and windows. Waste not included.
- Screws
- –Add a rate under Screws, tape and jointing compound rates.
- Joint tape
- –Add a rate under Screws, tape and jointing compound rates.
- Jointing compound
- 18.7 kgPacks of 20 kg: 1
Waste, door and window sizes
Extra for offcuts and breakages. 10% is a starting point, not a rule.
Screws, tape and jointing compound rates
The compound rate comes from the Siniat documents listed under Sources. Siniat gives no screws or tape per m², so those start empty: enter the figures for your own products to get a count.
No UK manufacturer figure found. Enter the rate for your product.
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Leave empty to skip the pack count.
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Estimate only. Check the product label and the building regulations where you live before you buy or build.
Quick answer
Add the wall area (room perimeter × wall height) and the ceiling area, take off doors and windows, add a waste allowance and divide by the area of one sheet: a 1200 × 2400 mm sheet covers 2.88 m². A 4 × 3.5 m room with 2.4 m walls, one door and one window has 46.76 m² to cover, which with 10% waste is 19 sheets of plasterboard, 13 for the walls and 6 for the ceiling.
How to use the plasterboard calculator
- Choose Room size to type the length, width and wall height of a room in metres (switch to Imperial for feet), or Areas to type wall and ceiling areas you measured yourself.
- Pick what you are boarding: walls and ceiling, walls only or ceiling only, and enter how many doors and windows the walls have.
- Choose the sheet size you plan to buy. The number of sheets, the area to cover and the jointing compound update as you type.
- Open Waste, door and window sizes to change the 10% waste allowance or the size of your openings. Open Screws, tape and jointing compound rates to add figures for your own screws and tape, or to change the compound rate.
How do you work out how much plasterboard you need?
Work out the area to cover, add a waste allowance, and divide by the area of one sheet. The wall area of a rectangular room is its perimeter times the wall height; the ceiling is length times width. Doors and windows come off the wall area because no board goes there.
Walls and ceiling are rounded up to whole sheets separately, because offcuts from wall sheets rarely fit the ceiling. Jointing compound is worked out from the area you cover, before waste: Siniat rates a 20 kg bucket of its ready-mixed compound at 50 m² for a full taping operation, which is 0.4 kg per m².
wall area = 2 × (length + width) × wall height − doors − windowsceiling area = length × widthsheets = area × (1 + waste %) ÷ area of one sheet, rounded upjointing compound (kg) = area × 0.4screws or tape = area × your rate per m²What size are sheets of plasterboard?
Standard 12.5 mm plasterboard comes 1200 mm wide in lengths of 2400, 2500, 2700 and 3000 mm, and as a smaller 900 × 1800 mm sheet, in Siniat’s product range. Siniat gives 8.0 kg per m² for its 12.5 mm standard board; the weights below are worked out from that figure.
| Sheet | Area per sheet | Sheets per 10 m² | Weight at 8.0 kg/m² |
|---|---|---|---|
| 1200 × 2400 mm | 2.88 m² | 3.47 | 23.0 kg |
| 1200 × 2500 mm | 3.00 m² | 3.33 | 24.0 kg |
| 1200 × 2700 mm | 3.24 m² | 3.09 | 25.9 kg |
| 1200 × 3000 mm | 3.60 m² | 2.78 | 28.8 kg |
| 900 × 1800 mm | 1.62 m² | 6.17 | 13.0 kg |
Siniat’s data sheet gives 23.0 kg for a 1200 × 2400 mm board in 12.5 mm, 17.3 kg in 9.5 mm and 28.8 kg in 15 mm.
Worked examples
Walls and ceiling of a 4 × 3.5 m bedroom
The room is 4 × 3.5 m with 2.4 m walls, one 90 × 200 cm door and one 120 × 120 cm window. The walls are 2 × (4 + 3.5) × 2.4 = 36 m². The door takes off 1.8 m² and the window 1.44 m², leaving 32.76 m². The ceiling is 14 m², so the area to cover is 46.76 m².
With 10% waste, the walls need 32.76 × 1.1 ÷ 2.88 = 12.51, so 13 sheets of 1200 × 2400 mm, and the ceiling 14 × 1.1 ÷ 2.88 = 5.35, so 6 sheets: 19 in all. At Siniat’s 0.4 kg per m², taping and jointing takes 18.7 kg of ready-mixed jointing compound, one 20 kg bucket.
Walls of a 5 × 4 m living room with 2.7 m ceilings
A living room is 5 × 4 m with 2.7 m walls, one door (90 × 200 cm) and two windows (120 × 120 cm), and only the walls get new plasterboard. The walls are 2 × (5 + 4) × 2.7 = 48.6 m², less 1.8 m² for the door and 2.88 m² for the windows: 43.92 m².
With 10% waste that is 48.31 m². In 1200 × 2700 mm sheets (3.24 m²) you need 48.31 ÷ 3.24 = 14.9, so 15 sheets, and each one fixed upright covers the full 2.7 m height with no joint across the wall. In 1200 × 2400 mm sheets you need 16.8, so 17. Either way the compound comes to 17.57 kg, one 20 kg bucket.
How much jointing compound do you need?
Plan on about 0.4 kg of jointing compound per m² of plasterboard for a full tape and joint, the rate of Siniat’s 20 kg ready-mixed compound. Siniat gives the coverage of each pack for a stated stage of the job; the last column divides the pack weight by that area.
| Compound | Pack | Coverage per pack | kg per m² |
|---|---|---|---|
| Ready-mixed, air-drying | 20 kg | 50 m², full taping operation | 0.40 |
| Ready-mixed, air-drying | 20 kg | 135 m², finishing coat | 0.15 |
| Powder, air-drying | 25 kg | 55 m², full taping operation | 0.45 |
| Powder, air-drying | 25 kg | 150 m², finishing coat | 0.17 |
| Powder, setting | 12.5 kg | 25 m², bedding and second coat | 0.50 |
| Powder, setting or air-drying | 10 kg | 25 m², bedding and second coat | 0.40 |
Siniat joint tape comes in 150 m rolls, 53 mm wide. Siniat gives no metres of tape per m², so the tape rate starts empty.
Should you tape and joint plasterboard or skim it?
Both work on standard plasterboard: taping and jointing dries sooner, and a skim coat suits boards that are not hung true. Siniat describes taping and jointing as quicker than a full plaster skim with less drying-out time, and a skim as particularly suitable where the quality of board installation is poor and drying time is not important. Its standard board takes a skim with no pre-treatment.
Tapered-edge boards are made for taping and jointing, because the tape sits in the taper below the finished surface; Siniat says square-edged boards may also be jointed. The jointing compound result is for taping and jointing only. If you skim, ignore it and work out the plaster from the coverage printed on the bag you buy.
Questions
How many sheets of plasterboard do I need for a room?
A 4 × 3.5 m room with 2.4 m walls, one door and one window needs 19 sheets of 1200 × 2400 mm plasterboard for the walls and ceiling, including 10% for waste: 13 for the walls and 6 for the ceiling. For any other room, add the wall and ceiling areas, take off the openings, add the waste allowance, divide by 2.88 m² and round up.
How many screws per sheet of plasterboard?
At least 27 screws for a 1200 × 2400 mm sheet on a wall with studs at 600 mm centres. Siniat gives 300 mm as the maximum screw spacing for linings and partitions: the sheet touches three studs, and 2400 ÷ 300 = 8 gaps means 9 screws on each. That is 9.4 per m², the lowest wall rate to enter. Ceilings need closer fixing: 150 mm at perimeters and cut edges, 230 mm in the field.
How much jointing compound do I need for plasterboard?
About 0.4 kg per m² for a full tape and joint, based on Siniat’s 20 kg ready-mixed compound covering 50 m². The walls and ceiling of a 4 × 3.5 m room (46.76 m²) take 18.7 kg, one 20 kg bucket. A finishing coat on its own uses far less: Siniat gives 135 m² per 20 kg bucket.
How heavy is a sheet of plasterboard?
A 1200 × 2400 mm sheet of 12.5 mm standard plasterboard weighs about 23.0 kg, according to Siniat’s data sheet, which gives 8.0 kg per m². The same size weighs 17.3 kg in 9.5 mm and 28.8 kg in 15 mm. A 900 × 1800 mm sheet of 12.5 mm board works out at about 13 kg, a lighter sheet to hold overhead on a ceiling.
What size is a sheet of plasterboard?
The standard sheet is 1200 × 2400 mm, which covers 2.88 m². Siniat also makes 1200 mm wide board in 2500, 2700 and 3000 mm lengths and a smaller 900 × 1800 mm sheet. Thicknesses are 9.5, 12.5 and 15 mm, though not every size comes in every thickness. A length that matches your ceiling height lets one sheet fixed upright cover the wall with no joint across it.
How long should plasterboard screws be?
At least the board thickness plus 25 mm when fixing to timber, and plus 10 mm into metal studs, according to Siniat: 37.5 mm or longer for 12.5 mm board on timber. Use coarse-thread screws for timber and fine-thread screws for thin metal studs, keep them at least 10 mm from bound edges and 13 mm from cut edges, and drive the heads until they sit slightly below the surface.
Sources
- Siniat (Etex), Plasterboard portfolio and drylining product range (leaflet) (checked 19 October 2026)Standard Board sizes: 12.5 mm × 1200 × 2400, 2500, 2700 and 3000 mm and 900 × 1800 mm, tapered or square edge; 9.5 and 15 mm sizes; jointing compound pack sizes and coverage.
- Siniat (Etex), Siniat drywall manual: Annexes, version 1.1.0, July 2022 (checked 19 October 2026)Jointing compound coverage per pack; joint tape 150 m × 53 mm; maximum screw spacing 300 mm on partitions and linings, 150 and 230 mm on ceilings; screw length and edge distances; skimming as an alternative to taping and jointing.
- Siniat (Etex), GTEC Standard Board technical datasheet (checked 19 October 2026)8.0 kg/m² and 23.0 kg for a 1200 × 2400 mm board in 12.5 mm; 17.3 kg in 9.5 mm and 28.8 kg in 15 mm; BS EN 520 Type A.
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