Calculate boards and screws needed from room dimensions

Rooms

Type Room / wall Length (m) Width (m) Height (m) Doors Windows Ceiling Board Boards
Wall area deducts a standard door (1.5m²) and window (1.44m²) allowance per opening - for non-standard openings, adjust the door/window counts to approximate the total area to deduct. Can't describe the room as a simple rectangle - an L-shape or other irregular layout? Add "Wall" rows instead of (or alongside) a "Room" row: each one is a single wall face entered directly by its own length, so an irregular room can be built up wall by wall. Wall rows have no ceiling of their own - add a separate Room row if the ceiling also needs boarding.
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Area (m²)
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Boards
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Screws
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Compound bags

Board layout, to scale

A representative wall, boards laid in a running bond - board counts use each row's Board size

Bill of materials

MaterialQuantity
Board counts include a 10% wastage allowance for cuts and offcuts. Screw counts assume standard wall/ceiling fixing centres; jointing compound assumes one coat over every board joint and screw head. A rough ordering guide, not a fixing specification - always confirm with your plasterboard supplier.

Board types, at a glance

Board typeSize (mm)Area per board (m²)
Pick the board size for each room or wall in the Board column on the Rooms tab - its board count uses that size, and new rows start at 1200 x 2400mm. Standard UK plasterboard sizes - actual sizes and thicknesses vary by manufacturer and application (wall, ceiling, fire-rated, moisture-resistant). Always check the board manufacturer's specification for the job.

Plasterboard calculator

This plasterboard calculator works out how many sheets of plasterboard you need, plus screws and bags of jointing compound. Enter each room's length, width and height in metres, the doors and windows, whether you're boarding the ceiling, and the board size: 2400 x 1200, 3000 x 1200 or 1800 x 900. For an L-shaped room, add each wall on its own.

It's free, works in your browser with no sign-up, and there's a free Windows app too.

Worked example: boarding a 4 m x 3.5 m bedroom, walls and ceiling

A 4.0 x 3.5 m bedroom, 2.4 m high, one door and one window, walls and ceiling boarded in the default 2400 x 1200 mm sheets (2.88 m2 each).

  1. Walls: 2 x (4.0 + 3.5) x 2.4 = 36 m2, less 1.5 m2 door and 1.44 m2 window = 33.06 m2.
  2. Ceiling: 4.0 x 3.5 = 14 m2. Total 47.06 m2 (shown as 47.1).
  3. Boards: 47.06 x 1.1 (10% waste) = 51.77 m2, divided by 2.88 = 17.97, rounded up to 18 boards.
  4. Screws: 33.06 x 20 per m2 on the walls + 14 x 25 per m2 on the ceiling = 1,011.2, rounded up to 1,012 screws.
  5. Jointing compound: 47.06 x 0.5 kg/m2 = 23.5 kg, so 1 x 25 kg bag.

Walls only, it needs 13 boards and 662 screws. In 3000 x 1200 boards, walls and ceiling take 15.

Questions

How many sheets of plasterboard do I need for a room?

Multiply the room's perimeter by its height, take off the doors and windows, add the ceiling area if you're boarding it, add about 10% for waste and divide by the area of one sheet (2.88 m2 for a 2400 x 1200 board). Round up to whole sheets. The calculator does this for each room, using the board size you pick for that room, and totals the boards for you.

How many 2400 x 1200 plasterboard sheets do I need for a 4 m x 3.5 m room?

With a 2.4 m ceiling height, one door and one window, the calculator gives 13 sheets for the walls only, or 18 sheets if you board the ceiling as well. Both figures include a 10% waste allowance.

Should I deduct doors and windows from plasterboard area?

The calculator takes off 1.5 m2 for each door and 1.44 m2 for each window. For a large opening such as patio doors, enter it as two or more doors or windows so the deduction is roughly right, or leave small openings in if you'd rather keep the offcuts as extra margin.

How many screws per sheet of plasterboard?

The calculator allows 20 screws per m2 on walls and 25 per m2 on ceilings, which works out at about 58 screws per 2400 x 1200 sheet on a wall and 72 on a ceiling. Ceilings get closer fixings because the boards hang overhead; check the board manufacturer's fixing centres for your job.

How much jointing compound do I need for plasterboard?

The calculator allows 0.5 kg per m2 for one coat over every joint and screw head, then rounds up to whole 25 kg bags, so one bag covers about 50 m2. Allow more if you're applying several coats.

How much waste should I allow for plasterboard?

The calculator adds 10% for cuts and offcuts, then rounds each room up to whole boards. Rooms with lots of openings, sloping ceilings or short wall runs can waste more, so round up generously there.

Plasterboard Calculator for Windows · More free construction calculators