What timber size and stud spacing does a partition wall need?

Stud spacing is not arbitrary — it comes from board sheet sizes. British plasterboard is 1200mm wide, which divides exactly by both 400 and 600, so board edges land on stud centres with no cutting. That is the whole reason those two numbers exist, and it is why setting out from one end matters more than the exact spacing.

Step by step

1. Choose the stud depth by what has to go inside the wall.A plain partition can be built in 63mm or 75mm timber. If the wall carries drainage, a concealed cistern, substantial insulation for sound, or services crossing each other, you need more depth — 89mm or 100mm — and it is far cheaper to decide now than to discover a soil pipe will not fit.
2. Use CLS or regularised timber for straightness.CLS is planed to a consistent section with eased edges and is the standard for studwork. Sawn timber is cheaper and less consistent in size, which shows up as an uneven wall face.
3. Set the spacing from the board width.Twelve hundred millimetre board divides into 400 or 600. Set the first stud so that its centre is 400 or 600 from the face of the end stud, and every board edge afterwards lands on a stud without measuring.
4. Default to 400mm centres unless there is a reason not to.It gives a noticeably stiffer wall, it supports 9.5mm board properly, it provides more fixing points, and the extra timber is a small proportion of the cost of the job.
5. Use 600mm centres where the wall is doing nothing demanding.With 12.5mm board on both faces, a partition in a domestic room that will carry nothing heavier than a picture is perfectly adequate at 600 centres, and it uses a third less timber.
6. Tighten the spacing where it matters.Behind tiling, in a bathroom, on a wall that will carry a wall-hung basin or a large TV, or where the wall will be knocked into regularly, 400mm centres or closer with generous noggins is worth the timber.
7. Match the board thickness to the spacing.Nine and a half millimetre board wants 400mm centres. Twelve and a half will span 600. Boarding thin over wide centres is what produces a wall that flexes visibly between the studs.
8. Check the timber before you build with it.Sight along every length. Bowed or twisted studs telegraph straight through the board and cannot be corrected once the wall is up, so sort them out on the floor and use the worst as noggins.

Tips

• Where a wall face has to be dead flat — behind a large mirror, a run of tiling, or a fitted wardrobe — pack the studs to a string line as you fix them rather than trusting the timber.
• Doubling the studs either side of a door opening is standard, and doing the same wherever something heavy will hang gives you a genuinely solid fixing point.
• If the partition is between two bedrooms and sound matters at all, spend the extra on deeper studs so there is room for insulation, and consider staggered studs so the two faces do not share the same timber.

Common mistakes

• Setting stud centres out from both ends — Whatever is left over ends up in the middle, so board edges no longer land on studs and every joint needs a noggin or a cut. Set out from one end and let the odd spacing fall at the far end.
• Measuring centres as gaps — Four hundred centres means 400mm from the centre of one stud to the centre of the next, not 400mm of clear space between them. Getting this wrong throws every board edge off.
• Using timber that is too thin to take services — A 63mm stud leaves very little room for a cable and no room for a waste pipe. Wall depth is decided by the services, not by the boarding.

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