Plasterboard Calculator

Plasterboard Calculator: Sheets for Walls and Ceilings

Plasterboard is the board you fix to stud walls and ceilings before skimming, taping or painting — and it is exactly the product that American sites call drywall. If you have been reading US advice in feet and inches, our Drywall Calculator covers the same job in imperial units. This page is the UK version: everything is metric, in metres and millimetres, and in the sheet sizes British merchants actually stock. Enter your room, pick a board size, add a sensible allowance for cuts and breakages, and the calculator gives you the area to board, the exact sheets that area needs, and the number you should actually order. No prices are involved — just honest sheet counts, so you neither run short on the day nor pay to store boards you will never use.

Quick answer

For a 4 × 3 m room with a 2.4 m ceiling, boarding the walls only, you need 12 sheets of 2400 × 1200 mm plasterboard — and 13 sheets once you add the standard 10% waste allowance. Board the ceiling as well and the same room needs 16 sheets net, or 18 to buy. The working is simple: the walls of that room come to 33.60 m², one big sheet covers 2.88 m², and 33.60 ÷ 2.88 = 11.67, which rounds up to 12 because merchants do not sell two-thirds of a sheet. Use the calculator below for your own room — it does the rounding, the waste and the ceiling for you.

How the calculation works

The calculator follows the same steps a plasterer works through with a tape measure, in the same order. First it finds the area to board. Then it divides that area by the coverage of one sheet. Finally it repeats the sum with your waste allowance added, because the first number is the least the room can take, not the number that gets the job finished.

• Walls only: (2 × length + 2 × width) × ceiling height — the perimeter of the room, multiplied by how tall it is.
• Walls + ceiling: the wall area above, plus length × width for the ceiling itself.
• Single wall: wall length × wall height, for one feature wall, a new stud partition or a repair.
• Sheets needed (net): area to board ÷ sheet coverage, rounded up to a whole sheet.
• Sheets to buy: area × (1 + waste %) ÷ sheet coverage, rounded up again.

The waste allowance is not padding for its own sake. Every doorway, socket cut-out and awkward corner eats board, sheet ends get damaged in transit and on stairs, and one mis-measured cut can ruin a board. Ten percent suits a plain rectangular room; allow 15% for rooms with several openings, sloping ceilings or a lot of boxing-in. This calculator does not deduct doors and windows — on real rooms the offcuts around openings rarely find another home, and counting the full wall is the safer, standard way to order.

Worked examples

Three examples, using the same figures the calculator gives, so you can check it by hand before you order.

• Walls only, 4 × 3 m room, 2.4 m ceiling: the perimeter is 14 m, so the walls are 14 × 2.4 = 33.60 m². 33.60 ÷ 2.88 = 11.67, so 12 sheets net; with 10% waste, 36.96 ÷ 2.88 = 12.83, so 13 sheets to buy.
• Walls + ceiling, same room: add the 4 × 3 = 12 m² ceiling for 45.60 m² in total. 45.60 ÷ 2.88 = 15.83, so 16 sheets net; with waste, 50.16 ÷ 2.88 = 17.42, so 18 to buy.
• Single wall, 5 m × 2.4 m, in 1800 × 900 mm sheets: the wall is 12.00 m² and each sheet covers 1.62 m². 12.00 ÷ 1.62 = 7.41, so 8 sheets net; with waste, 13.20 ÷ 1.62 = 8.15, so 9 to buy.

Board types and thicknesses

Plasterboard is not one product. The core changes with the job, and picking the wrong board for a wet or fire-sensitive room is a mistake you only find out about later.

• Standard board: the everyday choice for walls and ceilings in dry rooms — bedrooms, living rooms, hallways and studies.
• Moisture-resistant board: the green-core board with a water-repellent facing, made for bathrooms and kitchens where steam and splashes are part of daily life. It resists moisture but is not waterproof, so shower enclosures still need proper tanking or a tile backer board behind the tiles.
• Fire-resistant board: the pink-core board, with glass fibres that hold the core together for longer in a fire. It is the usual specification for garages, for some kitchen layouts, and for protected escape routes such as hallways and stairwells.

Thickness is the second choice. 12.5 mm is the standard for walls: stiff enough to feel solid, resistant to knocks, and the thickness most specifications assume. 9.5 mm board is lighter and slightly cheaper, and it is sometimes used on ceilings where the joists are closely spaced and weight matters, but it flexes more and is easier to damage. 15 mm board is the upgrade for fire resistance and sound insulation — noticeably heavier, and worth it on party walls and garage ceilings.

Fixing boards in brief

Boards are fixed one of two ways. On timber or metal studwork they are screwed to the studs, with plasterboard screws driven just below the paper surface without tearing it. On solid masonry they can be dabbed on: dabs of plasterboard adhesive on the wall, with the board pressed and levelled against them — faster than battening, but it needs a reasonably flat wall behind it. Ceilings are the heavy end of the job either way. A full 2400 × 1200 sheet in 12.5 mm weighs about 25 kg, and it has to be held flat overhead while it is fixed — that takes two people and board props, or a hired panel lift, never one person balancing a sheet on their head. Board the ceiling first, then the walls from the top down, stagger the joints, and keep every sheet a few millimetres off the floor so it cannot wick up damp.

What to calculate next

• Drywall Calculator — the US version of this page, in feet, inches and 4 × 8 ft sheets.
• Square Footage Calculator — work out the area of awkward rooms and shapes first; it also converts square metres.
• Paint Calculator — once the new boards are skimmed and sealed, work out how much paint the walls and ceiling will need.

Frequently asked questions

Estimates only — order one or two spare sheets; a damaged board should not stall the job.