Drywall / Plasterboard Calculator

Drylining and Plastering Guide

What should I know about Sheet Sizes?

Standard UK plasterboard is 2400 × 1200mm. 2700 × 1200mm suits 2.7m ceilings with no horizontal joints. Larger sheets reduce joints but are heavy (9.5mm = ~25kg, 12.5mm = ~33kg per sheet) — plan carefully for solo installation.

What should I know about Screw Spacing?

Fix drywall screws at 150mm centres along edges and 200–250mm across the field. Use 38mm screws for 12.5mm board to timber, 55mm for double boarding. Over-drive screws slightly below the surface without breaking the paper face.

What's the difference between Foil-Backed and Standard?

Foil-backed plasterboard provides a vapour barrier on external walls, reducing the risk of condensation within the wall structure. Standard board is used for internal partitions. Moisture-resistant (MR) board should be used in bathrooms and kitchens.

What's the key thing to understand about Safety and Regulations?

Most structural and electrical DIY work in England and Wales must comply with Building Regulations and is notifiable to local Building Control. Work that is not notifiable (like-for-like replacements, cosmetic changes) can be done without notification. Notifiable work done without approval is technically illegal and can cause problems when selling the property. Electrical work in most rooms requires a Part P competent person or Building Control inspection. Gas work must always be performed by a Gas Safe registered engineer — it is illegal for anyone else to carry out gas work in the UK, and using an unregistered installer invalidates both your home insurance and any warranty on the work. For structural changes (removing load-bearing walls, altering the roof structure), always get a structural engineer's assessment before starting, even for jobs that look straightforward.

What do I need to know about Fire and Moisture-Resistant Boards?

Standard plasterboard works well for most ordinary walls and ceilings, but certain rooms and situations call for a specific board type rather than the standard option, and using the wrong board can be both a performance and, in some cases, a building regulations issue. Moisture-resistant board, often with a green-tinted paper face, is designed for bathrooms, kitchens and utility rooms where humidity is higher, since standard board can absorb moisture over time and eventually soften, sag or encourage mould growth behind tiling or paint. Fire-resistant board, typically pink-faced and denser than standard board, is required in specific locations by Building Regulations, most commonly around integral garages where they adjoin the house, in some loft conversion stud walls and ceilings forming part of an escape route, and around certain fire-rated partition walls, where the extra density and glass-fibre reinforcement slow the spread of fire for a specified period. Using standard board in a location that building regulations require fire-rated board isn't just a technical shortcut, it can be flagged at building control sign-off or during a future property sale survey, so it's worth checking which board type applies to each room before ordering rather than defaulting to standard board throughout a project.

What should I know about Taping and Jointing Compound Quantities?

Once plasterboard sheets are fixed in place, every joint between boards, every internal and external corner, and every screw head needs taping and filling with jointing compound before the wall is ready to paint or paper, and this finishing stage needs its own separate material allowance beyond the board count this calculator produces. Joints are typically taped with either paper jointing tape bedded into a first coat of compound, or a self-adhesive mesh tape, then covered with two or three progressively wider coats of compound, each left to dry fully before the next, to build a flat, feathered-out joint that's invisible once painted. As a rough material guide, a typical stud-built room needs several bags of ready-mixed or powder jointing compound to finish all joints and screw heads properly, though this varies with how many boards and joints the room has, how much corner bead is used, and how many coats are applied. Rushing the drying time between coats, or skipping a final fine-sanding pass, is one of the most common reasons DIY plastered joints show through as faint ridges once a wall is painted, particularly under raking light from a window or downlight, since paint has a tendency to highlight rather than hide an imperfectly finished joint.

What do I need to know about Skim Coat Plaster Finish Over Drywall?

Plasterboard can be finished either by taping and filling the joints only (common in the US and for a 'ready for paint' finish) or by skimming the entire board with a thin coat of finish plaster, which is the more common approach in the UK for a smooth, durable wall. A skim coat is typically 2-3mm thick, applied in two passes with a finishing trowel, and needs the boards to be the right type — standard plasterboard with its ivory-coloured face is designed to be skimmed, while some moisture- or vapour-check boards need a specific primer (PVA or a proprietary bonding coat) before skimming will properly key to the surface. Joints should still be taped with scrim or paper tape and filled before skimming, not skipped, since skim plaster alone isn't strong enough to bridge a joint without cracking. New plasterboard, or boards with a very absorbent paper face, should be mist-coated with diluted PVA first so the plaster doesn't dry too fast and lose workability. Skimmed walls typically need a few days to fully dry before painting, and should be sealed with a mist coat of diluted paint before the final coats.

Reference: Sheets Needed by Room Size

These figures are for walls only at a standard 2.4m ceiling height; add ceiling area separately (length x width of the room) if boarding the ceiling too, and always round sheet counts up rather than down, since offcuts from one wall rarely fit cleanly onto another once window and door openings are deducted.

Worked Example: Material Take-Off for a Bedroom

A 3.5m x 3.5m bedroom with a 2.4m ceiling has a perimeter of 14m, giving a total wall area before openings of 14 x 2.4 = 33.6 m2. Deducting a standard door (0.8m x 2m = 1.6 m2) and one window (1.2m x 1.2m = 1.44 m2) leaves 33.6 - 1.6 - 1.44 = 30.6 m2 of boardable wall. Each standard 1.2m x 2.4m sheet covers 2.88 m2, so the raw sheet count is 30.6 / 2.88 = 10.6 sheets. Adding a standard 10-15% waste allowance for cuts and breakages brings this to roughly 12 sheets, which is also the practical number to order since suppliers do not sell part-sheets. Fixings follow the sheet count: at the recommended 150mm screw spacing on edges and 300mm in the field, a typical 1.2m x 2.4m sheet takes around 25-30 drywall screws, so 12 sheets need in the region of 300-360 screws — most trade boxes of 1,000 screws comfortably cover several rooms of this size, which is worth factoring into material ordering alongside the boards themselves.

What should I know about Drywall Delivery and Handling?

Standard 2.4m x 1.2m plasterboard sheets weigh around 20-24kg each for 12.5mm board, and a stack of 20-30 sheets is genuinely heavy enough to injure a back if carried incorrectly — sheets should be carried on edge, not flat, and ideally by two people for anything over about 10 sheets moved any distance. Most merchants will deliver and stack sheets inside the property on a kerb-side or ground-floor delivery, but upper-floor deliveries usually cost extra or require the fitter to carry sheets up manually, which is worth factoring into a quote comparison between suppliers, since a cheaper sheet price can be offset by a higher delivery charge.

What should I know about Ceiling vs Wall Board Thickness?

Ceilings are typically boarded with 12.5mm plasterboard on joists at standard 400-600mm centres, the same thickness commonly used on walls, but ceilings sometimes use thicker 15mm board, or require closer joist spacing, where a large unsupported span risks sagging over time. Getting ceiling fixing centres right matters more for sag prevention than for the board's stated fire or acoustic rating, since even a fire-rated board will sag visibly if screwed into joists spaced too far apart for its thickness.