What size screws for plasterboard?
The merchant's default is a 32 mm screw, and on a timber stud it is too short for every board thickness sold. The length is not a preference — British Gypsum specify the board thickness plus a minimum penetration into the frame, and that arithmetic lands on 38 mm for the board most people are hanging.
Quick answer
For 12.5 mm plasterboard on timber studs, use a 38 mm screw — not the 32 mm one most merchants hand you. British Gypsum specify the board thickness plus a minimum 25 mm penetration into timber, which comes to 37.5 mm and rounds up to the 38 mm size that is actually sold. A 32 mm screw leaves only 19.5 mm in the stud. On metal studs the figure is 25 mm, because only 10 mm of penetration is wanted — and one 25 mm screw is correct for 9.5, 12.5 and 15 mm board alike. For 15 mm board on timber, 42 mm.
| Board | Frame | Minimum penetration | Board + penetration | Buy |
|---|---|---|---|---|
| 9.5 mm | Timber stud | 25 mm | 34.5 mm | 38 mm |
| 12.5 mm | Timber stud | 25 mm | 37.5 mm | 38 mm |
| 15 mm | Timber stud | 25 mm | 40.0 mm | 42 mm |
| 9.5 mm | Metal stud | 10 mm | 19.5 mm | 25 mm |
| 12.5 mm | Metal stud | 10 mm | 22.5 mm | 25 mm |
| 15 mm | Metal stud | 10 mm | 25.0 mm | 25 mm |
Why 32 mm is short on timber
Subtract the board from the screw and what is left is what is holding in the stud. A 32 mm screw through 12.5 mm board leaves 19.5 mm in the timber where 25 mm is specified. Through 9.5 mm board it leaves 22.5 mm — still short. There is no single-layer board thickness for which a 32 mm screw meets the timber figure.
Nothing about the finished wall will tell you. The board goes up, the joints get taped, the paint goes on. What shows up later is popped screw heads along the lines of the studs, because a short screw is gripping the outermost fibres of the timber rather than biting into it properly, and the board moves against it.
Metal is the opposite problem. Only 10 mm of penetration is wanted, because the screw is cutting a thread in sheet steel rather than gripping wood fibre, and extra thread out the back of the stud catches on the services running inside it. One 25 mm screw is correct for 9.5, 12.5 and 15 mm board on metal — a single box covers every thickness. Use a fine-thread screw with a sharp point; a coarse-thread board screw will spin in a steel stud without ever pulling the board tight.
Double-layer boarding
The same rule, applied to the total thickness being screwed through. Two layers of 12.5 mm is 25 mm of board plus 25 mm into timber, so the face layer wants a 50 mm screw; two layers of 15 mm comes to 55 mm and takes the next size up, 63 mm. The base layer is fixed on its own, so it takes the single-layer length from the table above. Check what is inside the stud before using a 63 mm screw on a 47 mm stud — it will come out the back.
How many screws, and how much do they weigh
Screw count follows stud spacing rather than wall area: a sheet fixed to studs at 400 mm centres has more lines of fixing across it than the same sheet at 600 mm.
| Stud spacing | Per sheet | Screws | Weight |
|---|---|---|---|
| 400 mm centres | 30 | 414 | 0.5 kg |
| 600 mm centres | 22 | 304 | 0.4 kg |
Those counts assume 300 mm spacing along the board edges and 400 mm through the middle, which is ordinary practice for boarding out a room. A partition built to a British Gypsum system specification is tighter — 300 mm throughout, closing to 200 mm at external corners — so a specified partition takes meaningfully more screws than the figures above. If the wall has a fire or acoustic rating to meet, the system spec governs and not this table.
Screws are sold by weight as often as by count. At roughly 900 screws to the kilogram for a 38 mm coarse-thread, a 1,000 count box covers the room above twice over, and a 5 kg tub is about 4,500 screws — ten rooms. The tub is only the cheaper buy if you are boarding a whole house.
Where to put them
- At least 10 mm in from a bound edge, 13 mm from a cut edge. Closer than that and the screw breaks out through the paper, which is what is actually holding the board at that point.
- Ceilings are tighter than walls. A maximum of 230 mm in the field and 150 mm at the board ends — gravity works on a ceiling continuously, and a skim coat adds weight.
- Dimpled, not buried. The head should sit just below the surface with the paper intact around it. A screw driven through the paper has lost most of its grip and will need filling twice.
- Stagger the board joints so four corners never meet at one point. It costs a few more cuts and removes the crack that otherwise appears there first.
Common questions
Can I use drywall screws for anything structural?
No. Board screws are hardened and brittle by design — that is what lets them drive through steel and snap off flush rather than bend. In shear they fail suddenly and without warning. Anything carrying load, including a batten that will carry a cabinet or a TV bracket, needs a structural screw or a bolt.
What about screwing plasterboard to an existing plastered wall?
You are no longer fixing into a frame, so the thickness-plus-penetration rule does not apply. Dot-and-dab adhesive is the normal method; where screws are used it is through a plug sized to the substrate, and the length comes from the board plus the dab gap plus the plug. The fixings by substrate reference covers that case.
Do moisture-resistant and fire boards need different screws?
Not for length. The rule is the same arithmetic on the actual board thickness, and MR and fire boards come in the same 12.5 and 15 mm thicknesses. What does change is the spacing and sometimes the screw itself: fire-rated and acoustic construction is specified as a system, and the system's own figures override general practice.
Why round the length up rather than down?
Because the penetration figure is a minimum, not a target. Rounding 37.5 mm down to 32 mm takes you under it; rounding up to 38 mm leaves 25.5 mm in the timber, which satisfies it. The only limit on going longer is what is behind the stud.
Related
- Plasterboard calculator — your room, with the screw length worked out for the board and frame you pick
- Boarding out a room — one real room, every item on the order
- Fixings by substrate — what to use when there is no stud behind the plaster
- These tables as JSON — with the inputs that produced each row
Last reviewed 2026-10-17. Screw lengths and counts generated from the plasterboard calculator on this site; a test re-checks every figure above against the live tool on each build.
Sources and confidence
Every figure used on this page, what kind of figure it is, and where it came from. Figures marked as working estimates have no single authority behind them — they are the ones to check against your own supplier.
| Figure | Kind | Source | Note |
|---|---|---|---|
| Board thickness plus 25 mm into timber, 10 mm into metal | Published | British Gypsum technical FAQ, “What screw lengths do I use for fixing to metal and timber?” | Read at source. The specification is a minimum penetration, which is why the calculated length rounds up rather than down. |
| Screw lengths in the table, and the screw counts and weights | Derived | Generated from this site's plasterboard calculator | Produced by driving the calculator across every thickness and frame combination. A test re-checks each cell against the live tool on every build. |
| Edge distances: 10 mm from a bound edge, 13 mm from a cut edge; ceilings at 230 mm in the field and 150 mm at board ends; walls at 300 mm, 200 mm at external corners | Published | British Gypsum, The Site Book Good Practice Guide | Figures for GypWall partitions and CasoLine MF ceilings. A rated system's own specification overrides these. |
| 900 screws to the kilogram, and the 15% allowance in the counts | Working estimate | no primary source consulted | Trade practice for a 38 mm coarse-thread screw. Check against the box, which states a count. |
Derived Calculated from geometry. The formula is on this page. Published From a manufacturer data sheet or published standard, cited below. Working estimate Trade practice, rounded up. No single authority; the weakest category here.