Show the formula and working
This plasterboard calculator works out how many sheets of plasterboard you need to board the walls or ceiling of a room, how many drywall screws to buy and how long they should be. It is built for UK and European rooms measured in metres, with a feet and inches switch, and it uses the board sizes and fixing guidance that British Gypsum publishes for Gyproc boards.
Quick answer: Divide the area to board by the area of one sheet, then add about 10% for cutting. A 1200 x 2400 mm sheet covers 2.88 m², so a 4 m by 3.5 m room with 2.4 m walls, less 3.6 m² of doors and windows, needs 13 sheets. The plasterboard calculator also counts about 27 screws per wall sheet.
What Is a Plasterboard Calculator?
A plasterboard calculator is a tool that turns the size of the walls or ceiling you are boarding into a number of plasterboard sheets and fixings. Wall area is 2 x (length + width) x height; ceiling area is length x width. Subtract doors and windows from the walls, add a waste allowance, divide by the area of one sheet and round up.
Screws are counted per sheet from the frame spacing and the screw centres. British Gypsum guidance on screw lengths for fixing to metal and timber gives 300 mm centres on walls and 230 mm centres in the field of ceiling boards, and says the screw must be the board thickness plus at least 25 mm into timber or 10 mm into metal.
How Do You Use the Plasterboard Calculator?
- Choose What are you boarding?: all walls of a room, one wall or one ceiling.
- Enter Length, Width and Wall height, and tick Include the ceiling if you are boarding it too.
- Enter Doors and windows to leave out in square metres.
- Pick the Board size and Board thickness, and choose what you are Fixing into.
- Measure and enter Stud spacing (walls) and Joist spacing (ceilings), centre to centre.
- Adjust Extra for cutting and waste if the room has many corners, windows or a sloping ceiling.
- Read the sheets and screws, then open “Show the formula and working” to see each step with your numbers.
How Many Sheets of Plasterboard Do I Need for a Room?
An average 4 m by 3.5 m room with 2.4 m walls needs 13 sheets of 1200 x 2400 mm plasterboard for the walls and 6 more for the ceiling, including 10% for waste. As a rule of thumb, allow about 3.5 standard sheets for every 10 m² of wall before waste, or 3.8 sheets with waste.
Long walls and tall rooms often suit bigger boards. The Gyproc WallBoard 12.5 mm data sheet lists sizes from 900 x 1800 mm up to 1200 x 3600 mm, so a 2.7 m high wall can be boarded with 2700 mm sheets and no horizontal joints.
Plasterboard Sizes and Coverage
| Sheet size | Area per sheet | Sheets per 10 m² (no waste) | Weight of 12.5 mm WallBoard (at least) |
|---|---|---|---|
| 900 x 1800 mm | 1.62 m² | 6.17 | 12.5 kg |
| 900 x 2400 mm | 2.16 m² | 4.63 | 16.6 kg |
| 1200 x 2400 mm | 2.88 m² | 3.47 | 22.2 kg |
| 1200 x 2700 mm | 3.24 m² | 3.09 | 24.9 kg |
| 1200 x 3000 mm | 3.60 m² | 2.78 | 27.7 kg |
Weights use the minimum of 7.7 kg per m² that British Gypsum states for 12.5 mm WallBoard. Smaller 900 mm wide sheets are lighter and easier for one person to lift onto a ceiling.
How Many Screws per Sheet of Plasterboard?
A 1200 x 2400 mm wall sheet on studs at 600 mm centres takes about 27 screws: three studs with nine screws each at 300 mm centres. On a ceiling with joists at 400 mm centres and screws at 230 mm, a sheet takes about 49. British Gypsum also asks for closer screws at board ends on ceilings and at external corners, so buy a few extra.
For ceilings the calculator assumes the long edges run across the joists. Keep fixings at least 13 mm from cut edges and 10 mm from bound edges, as the data sheet advises.
What Length Screws for Plasterboard?
Plasterboard screws must be the board thickness plus at least 25 mm into timber or 10 mm into metal. That means 37.5 mm or longer for 12.5 mm board on timber, 40 mm for 15 mm board on timber, and 22.5 mm or 25 mm for 12.5 mm or 15 mm board on metal studs. Buy the nearest standard length above the minimum.
Once the boards are up, our paint calculator works out the emulsion for the finished walls, and if you are boarding a loft room the loft insulation calculator helps you plan the insulation behind it.
Worked Example: Boarding a Bedroom
Example: you are boarding the walls of a room 4 m long and 3.5 m wide with 2.4 m walls, using 12.5 mm boards of 1200 x 2400 mm on timber studs at 600 mm centres. The wall area is 2 x (4 + 3.5) x 2.4 = 36 m², less 3.6 m² for the door and window, which leaves 32.4 m². With 10% extra that is 35.64 m², and 35.64 / 2.88 = 12.4, so you need 13 sheets. Each sheet takes 3 x 9 = 27 screws, so 351 screws of at least 37.5 mm. These are the default inputs.
Plasterboard Calculator FAQs
What size is a standard sheet of plasterboard?
The standard UK plasterboard sheet is 1200 x 2400 mm, which covers 2.88 m². Smaller 900 x 1800 mm and 900 x 2400 mm sheets are easier to handle, and longer 1200 mm wide boards up to 3600 mm are made for tall walls. The common thicknesses are 12.5 mm and 15 mm.
Should I use 12.5 mm or 15 mm plasterboard?
12.5 mm board is the usual choice for walls and ceilings in homes. 15 mm board is heavier and stiffer, and it is used where a specification calls for better sound or fire performance. Check any building control requirements for your project before choosing.
How much does a sheet of plasterboard weigh?
A 1200 x 2400 mm sheet of 12.5 mm Gyproc WallBoard weighs at least 22.2 kg, based on the minimum of 7.7 kg per m² in British Gypsum’s data sheet. Thicker or special boards weigh more, so lifting ceiling boards is a two person job or needs a board lifter.
How much extra plasterboard should I buy?
Add about 10% to the area for a simple room, which covers offcuts around doors, windows and sockets. Allow 15% or more for rooms with many openings, alcoves or sloping ceilings. Spare offcuts are useful for small patches and boxing in pipes.
Do I subtract doors and windows when measuring for plasterboard?
Yes, take the area of doors and windows off the wall area, but remember that window reveals and the strips above doors still need boarding. The waste allowance usually covers those narrow pieces, so subtracting the full opening area is fine for most rooms.
How far apart should plasterboard screws be?
British Gypsum gives 300 mm centres for screws on walls and partitions, with 200 mm at external angles. On ceilings the centres are 230 mm across the board and 150 mm at the board ends. Use the closer centres on ceilings, where the boards hang from their fixings.
Checked October 2026. Sources: British Gypsum: Gyproc WallBoard 12.5 mm product data sheet, British Gypsum: What screw lengths do I use for fixing to metal and timber?