What this calculator works out
Boarding a room comes down to an area, a sheet size and a fixings list. This tool takes a room's length, width and height, or a wall area you already know, works out how much needs boarding once doors and windows are taken off, and turns that into sheets to buy for a UK or US board size, the screws or adhesive that hold them up, and the tape and compound to finish the seams.
It's a plasterboard and drywall quantity tool, not a plastering or skim-coat calculator: this covers hanging the board and taping the joints ready for a skim or paint-grade finish, not the finishing coat itself. For the room's floor, see the square footage calculator; for painting the finished walls, see the paint calculator.
How the maths works
Wall area starts the way the paint calculator works it out: the room's perimeter, the distance around all four walls, multiplied by the height. A 4m by 3.5m room has a 15m perimeter (2 × (4 + 3.5)), which at 2.4m high is 36 m² before anything is taken off. A direct area entry skips this step, and an optional ceiling toggle adds the floor area (length × width) on top, since a boarded ceiling is bought and fixed the same way as a wall.
Doors and windows come off next, at the same 1.9 m² (20 sq ft) per door and 1.4 m² (15 sq ft) per window used across this site's other room calculators, sensible averages rather than a measurement of your own opening. If deductions add up to more than the wall area, the total board area is held at zero rather than going negative.
Boards to buy is the total area divided by the chosen board's own area, plus the wastage allowance, rounded up, since no merchant sells part of a sheet. This is an area-based estimate rather than a cut-by-cut layout plan: real sheets get turned and positioned to land joints sensibly, which a plan drawing does better than an area sum, but the wastage allowance covers the difference for a shopping list.
Working the default through: 36 m², minus 3.3 m² for one door and one window, leaves 32.7 m² to board; a 2400×1200mm board covers 2.88 m², so 32.7 ÷ 2.88 = 11.35 boards before wastage, × 1.10 at the 10% setting is 12.49, rounded up to 13 boards.
Choosing a UK or US board size and thickness
British Gypsum's Gyproc WallBoard, the UK's most common range, is sold in a 2400 × 1200mm standard sheet and a smaller 1800 × 900mm "handy board" for tighter spaces or a single pair of hands, both in 9.5mm, 12.5mm and 15mm. In the US, drywall is sold by the sheet: 4 × 8ft (32 sq ft) is the standard size at Home Depot and most lumberyards, with 4 × 12ft (48 sq ft) a common longer option that cuts down horizontal joints on a tall wall; 1/2in is the standard thickness, roughly matching the UK's 12.5mm.
9.5mm board is lighter and easier to handle overhead or when re-boarding over sound existing plaster, but it flexes more between studs, so it isn't the first choice for a new stud wall. 12.5mm is the standard choice for new stud walls and most ceilings, with 15mm reserved for extra sound or fire resistance. Thickness doesn't change the board count here, since a sheet covers the same area whatever its thickness; the select above is guidance only.
A worked example, in UK and US prices
A bedroom, 4m by 3.5m, walls 2.4m high, one door and one window, standard 2400×1200mm board, 10% wastage, screwed to studs: 36 m² less 3.3 m² for the door and window leaves 32.7 m², needing 13 boards. Screws at roughly 10.4 per m² come to about 341, one box of 1000; tape at roughly 1.64 metres per m² comes to about 54 metres, one 90m roll; compound at 0.4 kg/m² comes to about 13 kg, two 12.5kg bags. At around £13 a board, 13 boards comes to about £169 before screws, tape and compound.
The American equivalent: a 12ft by 12ft room, walls 8ft high, one door and one window, 4×8ft sheets, same 10% wastage: the wall area works out to about 384 sq ft (35.7 m²) before deductions, 349 sq ft (32.4 m²) after, needing 12 sheets. At around $12 a sheet, that's about $144 before fixings.
Screws to studs, or dot and dab
Screwing to timber studs or metal battens is the standard fixing for a stud partition or a wall being re-framed: this calculator uses about 30 screws on a standard 2400×1200mm board, roughly 10.4 per m², based on British Gypsum's published screw-centre guidance for partition linings (roughly 300mm centres along each stud line), close to the US convention of about one screw per square foot on 16in on-centre framing, around 32 screws on a 4×8ft sheet. Screw counts are the same across both fixing methods for a boarded ceiling, since dabs are never used overhead.
Dot and dab bonds the board straight to a masonry wall with blobs of gypsum adhesive instead of a timber frame, common in the UK for boarding onto brick or block where studwork would eat into the room unnecessarily. A 25kg bag, such as British Gypsum's Gyproc DriWall Adhesive or Knauf's equivalent, covers roughly 4.2 to 4.6 m² per bag by Knauf's own published coverage, this calculator's default. Dot and dab is a wall-only method; a boarded ceiling always needs screwing to joists or battens, so switching still adds a separate screw count for any ceiling area included above.
Joint tape and jointing compound
Every joint between boards, and every internal angle, gets a strip of joint tape bedded in compound before filling, to stop the seam cracking as the building settles. This calculator uses about 1.64 metres of tape per m², based on a widely used US estimating rule of roughly one foot of tape per two square feet of board, about 16ft on a 32 sq ft (4×8ft) sheet. Tape rolls default to 90m, a common UK scrim tape length; British Gypsum's own paper tape comes in 150m rolls, so adjust the field to match whatever you're buying.
Jointing compound is counted here as a taping-coat allowance, enough to bed the tape and fill the joints, not a full three-coat skim across the whole board. 0.4 kg per m², about 8 lb per 100 sq ft, sits within the 5 to 14 lb per 100 sq ft range quoted across US drywall-estimating guides for a single application; a full skim or a paint-ready finish typically needs two to three times as much again. Bags are counted in the UK's common 12.5kg size, such as British Gypsum's Gyproc Joint Filler; in the US, compound is more often sold by the bucket, commonly a 4.5-gallon pail weighing 48 to 61lb depending on the product's weight class.
Moisture-resistant and other special boards
Standard plasterboard isn't the right choice everywhere. Moisture-resistant board, usually green-faced, belongs in bathrooms, kitchens and anywhere else with regular condensation or splashing, though it still isn't a tanking product and needs a proper waterproof membrane behind tiling in a shower or wet room. Fire-rated (pink) board suits a garage wall shared with living space or an escape route needing extra fire resistance, and sound-rated, denser board suits a party wall or a home cinema room. This calculator's sizes and thicknesses apply to standard, moisture-resistant and fire board alike; only the facing and core differ, not the sheet dimensions used for counting.
Questions people ask
Should I use 12.5mm or 9.5mm plasterboard?
12.5mm is the standard choice for a new stud wall and most ceilings, with enough rigidity to resist knocks between studs. 9.5mm is lighter and easier to handle overhead or when re-boarding over sound existing plaster, but it flexes more and isn't the first choice for a new partition. Thickness doesn't change how many boards you need for a given area, only the guidance on where to use it.
Where should I use moisture-resistant board?
Bathrooms, kitchens, utility rooms and anywhere else with regular condensation or splashing. It's usually green-faced and more resistant to damp than standard board, but it isn't a waterproof tanking system on its own; a shower or wet room still needs a proper waterproof membrane behind any tiling.
Dot and dab or screwing to battens, which should I use?
Dot and dab, bonding board straight to masonry with adhesive dabs, suits a solid brick or block wall in reasonable condition and avoids losing room space to a frame. Screwing to battens or studs suits an uneven wall that needs packing out flat first, a wall carrying real weight, or any wood-framed partition, since a stud wall has no masonry to dab onto. A boarded ceiling always uses screws into joists or battens; dabs are never used overhead.
How many screws does a plasterboard wall need?
About 30 screws on a standard 2400×1200mm board, roughly 10.4 per square metre, based on British Gypsum's published screw-centre guidance of around 300mm spacing along each stud line for partition linings. That's close to the US convention of about one screw per square foot on 16in on-centre framing, around 32 screws on a 4×8ft sheet.
How much wastage should I allow for plasterboard?
10% covers a straightforward rectangular room. Raise it to 15% for a room with lots of door and window openings to cut around, an awkward alcove or dormer, or a sloped ceiling, since offcuts from an angled cut rarely reuse cleanly elsewhere.
Is taping the joints the same as plastering?
No. Taping and filling the joints, what this calculator's compound figure covers, gets the board ready for either a full plaster skim or a paint-grade "tape and float" finish sanded smooth. A full skim coat across the whole board uses two to three times as much compound as the taping allowance here, and is usually priced and bought as a separate job.
Board sizes are checked against British Gypsum and Travis Perkins listings for the UK, and USG and Home Depot listings for the US. Screw-centre guidance follows British Gypsum's published FAQ for partition linings, cross-checked against common US 16in on-centre drywall conventions. Tape and compound rates follow widely used US drywall-estimating conventions; adhesive coverage follows Knauf's published bag coverage. Real figures vary by supplier, wall condition and product, so treat this as a planning estimate and round up when buying.