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Plasterboard screw length: add the board, then size

Updated: 22 October 2026

You know the board thickness and whether the studs are timber or light metal. Plasterboard screw length is then a sum, not a brand. Add the board to the purchase in the frame, then buy the next stock size. A 12.5 mm sheet does not take the same screw on timber as on light metal. Centres stay on [how to screw plasterboard](/hub/screws-and-accessories/drywall-screws/sub/drywall-screws-how-to-fix-plasterboard). Thread stays on [coarse versus fine plasterboard screws](/hub/screws-and-accessories/drywall-screws/sub/drywall-screws-coarse-vs-fine). The nine boxes are on the [drywall screws comparison](/hub/screws-and-accessories/drywall-screws).

You know the board thickness and whether the studs are timber or light metal. Plasterboard screw length is then a sum, not a brand. Add the board to the purchase in the frame, then buy the next stock size.

Our top picks

Forgefix ForgeFix coarse 3.5 x 38 mm

Best overall

Forgefix ForgeFix coarse 3.5 x 38 mm
9.4/10about £2.57
View offer
TIMCO TIMCO 3.5 x 50 mm

Alternative

TIMCO TIMCO 3.5 x 50 mm
7.2/10about £6.01
View offer
Forgefix Forgefix 4.2 x 100 mm

Best value

Forgefix Forgefix 4.2 x 100 mm
8.6/10about £3.59
View offer
On this page
  1. 1.The two sums
  2. 2.Single boards and the next stock size
  3. 3.A second layer or a thick lining
  4. 4.Lengths on the cards in this set

The two sums

British Gypsum’s screw-length FAQ, for their screws, is the rule. The screw is the board thickness plus at least 25 mm into timber, or plus at least 10 mm into metal. Buy the next stock length that meets that sum. A 12.5 mm sheet on timber is 12.5 plus 25, which is 37.5 mm, so 38 mm coarse fits. On light metal, 12.5 plus 10 is 22.5 mm, so 25 mm fine is the stock size. A 25 mm or 32 mm screw on 12.5 mm board over timber leaves too little in the wood. Insulated plasterboard and dot-and-dab are not this sum.

Single boards and the next stock size

On timber, 12.5 mm is about 38 mm coarse. NHBC Standards 9.2.4 table 8 lists 38 mm for 12.5 mm into timber and 35 mm for 9.5 mm. On metal, NHBC lists 25 mm for a single board into steel. That 25 mm screw is for light metal only. Fifteen millimetres on timber is 15 plus 25, which is 40 mm, so about 42 mm if you keep the full purchase. NHBC lists 40 mm. An older British Gypsum Site Book table lists 38 mm. Do not average 38, 40 and 42. If a system sheet names one length, the sheet wins.
Forgefix ForgeFix coarse 3.5 x 38 mm

Testsieger

Forgefix ForgeFix coarse 3.5 x 38 mm
9.4/10about £2.57
View offer

A second layer or a thick lining

A second 12.5 mm board on timber is 50 mm if you keep 25 mm of purchase. NHBC lists 50 mm for two layers of 12.5 mm into timber, 60 mm for two of 15 mm, and 35 mm and 40 mm into steel. TIMCO’s 3.5 x 50 mm card matches that timber length only if the screw is coarse. Its page for 00050DRYS describes fine thread for track up to 0.6 mm, and the Amazon fields disagree. Forgefix 4.2 x 100 mm is the long coarse box when 50 mm is not enough.

Lengths on the cards in this set

Jiahezhi M4 x 25 mm, at £6.99, fails 12.5 mm board on timber, and the card is coarse. Wavanta is titled M4 x 30 mm, at £9.99, still short, and one UK review describes 16 mm screws. ForgeFix coarse 3.5 x 38 mm, 200 at £2.57, matches 12.5 mm board on timber. SEQUAL is also 38 mm and titled fine, which is long for a 25 mm metal sum unless the system asks for 38 mm. If the title and a bullet disagree, measure one screw from the parcel. The buying order around that measurement is the plasterboard screw buying guide. None of these lengths is a fire rating.

Common questions

What length for 12.5 mm board on timber?
About 38 mm of coarse screw. The board plus at least 25 mm into the timber is 37.5 mm, and 38 mm is the stock size that meets it. NHBC lists 38 mm for that cell. In this set the ForgeFix coarse 3.5 x 38 mm box is that length. A 25 mm or 30 mm screw on the same timber leaves too little in the stud.
What length for 12.5 mm board on metal studs?
About 25 mm of fine thread. The board plus at least 10 mm into the metal is 22.5 mm, so 25 mm is the next stock size. NHBC lists 25 mm for a single board into steel. That screw is not the timber screw. British Gypsum’s metal purchase is for their screws into Gypframe, and a thicker steel stud needs a self-drilling point rather than a longer needle.
What length for 15 mm board?
On timber, 15 mm plus 25 mm is 40 mm, so about 42 mm if you step to a common stock size and keep the full purchase. NHBC lists 40 mm. An older Site Book table lists 38 mm, which is slightly under 25 mm in the wood. On metal, keep the plus-10 mm rule and the system sheet. Do not treat 38, 40 and 42 as the same screw.
What length for a second layer?
About 50 mm into timber for a second 12.5 mm board, if you still want 25 mm of purchase. NHBC lists 50 mm for two layers of 12.5 mm into timber and 60 mm for two layers of 15 mm. Into steel the same table lists 35 mm and 40 mm for those two build-ups. A merchant cell of 42 mm for two 12.5 mm layers on timber leaves about 17 mm in the wood. Do not use it.
Is 25 mm or 32 mm enough on timber?
Not for 12.5 mm board. Twenty-five millimetres leaves about 12.5 mm in the stud. Thirty-two millimetres, sometimes sold against 9.5 mm board, is still under 25 mm of purchase behind 12.5 mm. Jiahezhi at 25 mm and Wavanta’s 30 mm title are the short cards in this set. One Wavanta review describes 16 mm, which does not clear the board.
Does a 75 mm screw replace a 100 mm screw?
Only if the build-up needs 75 mm and the screw in the bag is 75 mm. The Forgefix card titled 4.2 x 75 mm carries a bullet that says 100 mm, and it shares its review text with the 100 mm ASIN. The 100 mm box is the long coarse screw for a thick lining. Measure before you treat either title as the length you will drive. A fire or acoustic system uses its own sheet, not the longer of two conflicting bullets.

Related pages

Best plasterboard screws in this set

Drywall screws

Plasterboard screw buying guide: stud first, then box

Coarse vs fine plasterboard screws: timber or metal

How to screw plasterboard without tearing the paper

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk listing lines captured on 19 October 2026. The high-street price band that day is a rule of thumb and is not one of these rows. There is no laboratory pull-out test.

  1. British Gypsum 45 mm drywall screw data sheet (retrieved 19 October 2026)
  2. British Gypsum, screw lengths for metal and timber (retrieved 19 October 2026)
  3. British Gypsum, screw fixing centres (retrieved 19 October 2026)
  4. Knauf UK plasterboard screws (retrieved 19 October 2026)
  5. Speedline fixings sheet, August 2022 (retrieved 19 October 2026)
  6. Homebuilding, screwing into plasterboard (retrieved 19 October 2026)
  7. Wickes plasterboard screws (retrieved 19 October 2026)