Plasterboard & Drywall Calculator

Plasterboard Guide

What should I know about Standard Sheet Sizes?

Standard UK plasterboard is 2400×1200mm (8×4 feet). This covers 2.88 m² per sheet. Also available: 2700×1200mm, 3000×1200mm, and 900×1800mm (for tight spaces). Standard thickness: 9.5mm for ceilings (lighter weight), 12.5mm for walls, 15mm or 19mm for fire-rated partitions. Moisture-resistant (MR, pink or green board) for kitchens and bathrooms. Impact-resistant for high-traffic areas. Fire-resistant (pink board, Fireline) for fire separation requirements.

What should I know about Screw Spacing?

Timber stud walls: screws at 300mm centres along each stud, 150mm centres on perimeter edges. Maximum 50mm from sheet edge, minimum 10mm. Use drywall screws: 25mm for 9.5mm board on timber, 38mm for 12.5mm board. Metal stud partitions: use wafer-head self-drilling screws. Dot and dab (directly to masonry): use 100mm+ screws into wall plugs at 600mm centres. One 500-screw tub typically covers approximately 15–20 sheets. Count linear metres of stud or batten to calculate screws precisely.

What's the key thing to understand about Finishing Joints?

All tapered (long) edges are jointed with paper tape and jointing compound applied in three coats (filling, topping, finishing), feathered out 200–250mm either side of the joint. Cut (short) edges need to be rebated or chamfered before taping, or use scrim tape with a flexible filler. Each coat must be fully dry before the next — typically 12–24 hours. Sand lightly between coats with 120-grit. Skim plaster over the entire surface gives the best finish but requires plastering skills; using a fine a fine surface filler over standard joint tape and compound is usually sufficient for most walls.

What do I need to know about Sound and Thermal Insulation?

Standard plasterboard provides minimal sound or thermal insulation on its own. For party walls (between properties): use acoustic plasterboard, double layers, or resilient bar systems. For thermal: insulated plasterboard (PIR foam bonded to board, 25–50mm total) significantly improves wall U-values for dot-and-dab applications. For fire separation (Building Regulations Part B): two layers of 12.5mm standard board or one layer of 15mm fire-resistant board on each side of a stud partition provides a useful improvement in both sound insulation and fire resistance over standard 12.5mm board.

What do I need to know about Board Thickness Choices?

Plasterboard is available in several standard thicknesses, and choosing the right one for the application matters for both performance and how the board handles during fitting, beyond the sheet count this calculator estimates. The thinner common thickness, often used for lining over an existing sound surface or for curved work where board needs to flex slightly, is more flexible but offers less rigidity and sound insulation on its own. A mid-range thickness is the standard default for most new stud walls and ceilings, giving a reasonable balance of strength, ease of handling, and a surface that doesn't flex noticeably underfoot or when leant on. A thicker board, sometimes used on ceilings to span between joists at wider centres without sagging, or on walls where extra rigidity or sound insulation is wanted without going to a double-board layer, is heavier and harder for one person to lift and fix alone, particularly overhead on a ceiling, where a second pair of hands or a board lift tool makes a real practical difference. Matching board thickness to joist or stud spacing is also important structurally, since a board that's too thin for the span it needs to cover between fixing points can sag or crack over time even if it was fitted correctly.

What should I know about Handling and Storage Before Fitting?

Plasterboard is surprisingly easy to damage before it's even fitted, and poor handling or storage on site is a common, avoidable source of wasted sheets on top of the quantity this calculator estimates. Sheets should always be stored flat, fully supported along their length on a level surface or stack of battens, rather than leant upright against a wall for any length of time, since an upright sheet can bow or crack under its own weight, particularly in damp or humid conditions where the paper facing can absorb moisture unevenly. Boards should be kept dry and ideally brought into the room they'll be fitted in a day or so before fitting, similar in principle to acclimatising flooring, so the board's moisture content settles close to the room's actual conditions rather than fitting a board straight from a cold, damp delivery into a warm, dry room where it may subsequently shrink slightly at the joints. When carrying sheets, carrying them on edge rather than flat, and with the paper face protected from scraping against rough brickwork, blockwork or door frames, reduces the risk of damaged corners and torn paper facing, both of which weaken a sheet and make a clean, flat joint harder to achieve once it's fixed in place.

What should I know about Dot-and-Dab vs Mechanically Fixed Plasterboard?

Plasterboard can be fixed to a wall in two main ways, and the method affects both material requirements and suitability. Dot-and-dab involves fixing boards directly to masonry using blobs of plaster adhesive (bonding compound) applied in a pattern of dots and continuous dabs, without any timber or metal frame behind — this is the standard method for dry-lining solid masonry walls, and it's faster than building a frame, but it needs a reasonably flat, sound wall and isn't suitable over timber stud walls or where there's a risk of damp bridging through the adhesive dabs. Mechanically fixed plasterboard — screwed to timber studs, battens, or a metal frame — is used for stud partition walls, ceilings, and any situation needing more robust fixing, such as walls that will carry significant hung loads, or where sound/fire-rated assemblies require specific fixing patterns tested as part of that rating. Dot-and-dab generally uses less board waste since boards go straight onto a flat wall, while framed/mechanically fixed work needs the frame itself calculated and bought in addition to the board quantity. Mixing the two methods inconsistently across a room (dot-and-dab on one wall, battens on another) is fine, but each wall's fixing method should be decided before ordering adhesive or screws, since the quantities differ substantially.

Reference: Board Thickness and Where Each Is Used

Thicker and double-layer boards both add mass, which is the main driver of sound insulation between rooms — a single layer of 12.5mm plasterboard on a stud wall gives only modest sound reduction, while two layers with a staggered joint pattern and mineral wool insulation in the void can markedly cut noise transfer between, say, a bedroom and an adjoining home office.

Worked Example: Boarding a Stud Partition Wall

A new stud partition wall measures 4m long by 2.4m high, boarded on both sides (two faces, since it divides two rooms), using standard 2.4m x 1.2m tapered-edge boards. Area per face = 4 x 2.4 = 9.6 m2 Total area both faces = 19.2 m2 Sheet coverage = 1.2 x 2.4 = 2.88 m2 per board Raw board count = 19.2 / 2.88 = 6.7, rounded up to 7 boards, plus a 10% cutting allowance brings the practical order to 8 boards At the standard fixing pattern (screws every 150mm along board edges, every 300mm through the middle, into studs typically spaced at 400 or 600mm centres), this wall needs enough drywall screws for roughly 8 boards — in the region of 190-220 screws — plus joint tape and roughly one 25kg bag of jointing compound for taping and a basic two-coat finish on a wall this size.

Fire-Rated and Moisture-Resistant Boards: When You Need Them

Standard plasterboard is fine for most living spaces, but certain rooms and structural elements call for a specialist board, and using the wrong type can create a building regulations issue rather than just a cosmetic one. Moisture-resistant (MR) board, usually tinted green, is designed for bathrooms, kitchens and utility rooms where humidity is routinely elevated, resisting mould growth better than standard board though it is not fully waterproof and shouldn't be used as a tanking layer in wet zones like shower enclosures. Fire-rated board, usually tinted pink or red, contains glass fibre reinforcement that slows fire spread and is required by building regulations around certain escape routes, garage-to-house party walls, and some loft conversions. Acoustic plasterboard, denser than standard board, reduces sound transmission between rooms and is popular in converted flats or home cinema rooms. Always check current building regulations for the specific room and structure before assuming standard board will pass inspection, since requirements vary by room type and by how the space is used.