An 8 foot wall is 97-1/8 inches
This is the number that surprises people, and it explains something they have probably noticed. Switch the tool to feet and inches and it works to American framing, where the wall is a sole plate, the studs, and a double top plate.
Three plates at 1-1/2 inches each is 4-1/2 inches of the wall height gone before a single stud. Mills precut studs at 92-5/8 for this, and 92-5/8 plus 4-1/2 is 97-1/8. So a framed 8 foot wall stands 8 feet 1-1/8, and the extra inch is not sloppiness: it is what lets a 96 inch sheet of drywall go up above a finished floor with a gap at the bottom.
The 92-5/8 is a market convention rather than a code requirement, which is why the tool describes it as what mills cut rather than as a rule. The double top plate is the part the code actually asks for.
Where the code caps the height
Table 2308.5.1, which the IRC carries as R602.3(5), sets what a stud can do:
- 2x4, up to 14 feet non-bearing, 10 feet carrying a roof or one floor, 24 inch centres.
- 2x6, up to 20 feet non-bearing, 24 inch centres.
- 2x3, 16 inch centres only, and not permitted in an exterior bearing wall.
The distinction the tool keeps separate is bearing against non-bearing, because a 12 foot 2x4 partition is ordinary and a 12 foot 2x4 wall holding a roof up is a different conversation. It warns about the second and does not pretend to resolve it.
The one place inches are easier than millimetres
A 48 inch sheet is exactly three bays at 16 inch centres or two at 24. It always lands on a stud, because the framing module and the sheet size were designed as one system.
Metric has no such luck. A 1200mm board divides by 400 and 600 and does not divide by 450 or 500, so a wall framed at 450 leaves board edges floating in mid air with nothing to fix to and a joint that cracks. The British side of this tool warns about that, and the American side never has to.
A 3.6m wall at 600 centres has seven studs
Not six. Six is what length divided by centres gives you, and six is the number of gaps.
Studs are fence posts, not fence panels. One at each end and five in between. The missing one is always the last one, at the far end, and it is the one holding up the edge of a plasterboard sheet.
Every stud wall calculator that returns length over centres is one stud short on every wall it has ever been asked about. So this one shows both numbers: the bays, and the studs, so you can see where the extra one goes rather than just being told a different answer.
Same arithmetic as fence posts, joists, and anything else spaced along a line. It catches people every time because the division feels like the whole sum.
The board has to break on a stud
A plasterboard edge that lands between studs has nothing behind it to fix to. It flexes, the joint moves, and the crack comes back however many times it gets filled.
So the board width has to be a whole number of bays. 1200 divides by 400 into three bays and by 600 into two. Both fine.
It does not divide by 450 or 500, and people do occasionally set out at those for reasons that made sense at the time. The tool checks and says so, which is a great deal cheaper than finding out halfway through boarding.
Cut the noggins to the gap, not the centres
A noggin between studs at 600 centres is not 600 long. It is 562: the centres less the thickness of one stud.
Written down that is obvious. It is also a very easy thing to cut a whole pack of wrong on a chop saw with the stop set, and you do not find out until you go to fit the second one.
One per bay per row. Over about 2.4m high, two rows is usual: partly to stiffen the studs against buckling, partly to give a fixing wherever the boards break horizontally.
What it hands to the cutting list
The output is a set of lengths and quantities: studs at wall height, noggins at the clear gap, plates at wall length. Take those straight to the cutting list and it will work out which stock lengths to buy and how to cut them, including the saw kerf, which is the reason three 1200s do not come out of a 3600 board.
Whether the wall is loadbearing is not ours to answer
It does not decide whether the wall is loadbearing, what it can carry, what it needs for fire resistance or sound. Those are design and Building Regulations questions.
It does not size the header over an opening either. Two extra studs per opening are allowed as a trimmer each side, which is a working allowance rather than a setting-out, and what goes over the opening depends on what is above it, which is somebody else's call.
Next to it: plasterboard and skim for the finishing side, and timber grades.
Common questions
How many studs do I need?
Length divided by the centres, plus one. A 12 foot wall at 16 inches on center is 144 over 16, which is 9 bays, so 10 studs. The plus one is the stud at the far end and it is the one almost every calculator drops: studs are fence posts, not fence panels. Then add two per opening for the king and jack studs either side.
Why is a precut stud 92-5/8 inches and not 96?
Because a wall is not just studs. There is a sole plate underneath and a DOUBLE top plate on top, which in nominal 2 inch lumber is three plates at 1-1/2 each, so 4-1/2 inches of the height is plate. Add 92-5/8 to that and the framed wall stands 97-1/8, which is 8 feet 1-1/8. The extra inch is deliberate: it leaves room for a 96 inch sheet of drywall to go up above a floor covering with a gap at the bottom. So an 8 foot wall is not 8 feet, and that is the answer to why the ceiling in an American house measures a shade over.
Can studs be 24 inches on center?
For a 2x4 or a 2x6, yes, up to the height limits. Table 2308.5.1, which the IRC carries as R602.3(5), gives a 2x4 up to 14 feet as a non-bearing wall and 10 feet carrying a roof or one floor, both at 24 inch centres, and a 2x6 up to 20 feet non-bearing. A 2x3 is different: 16 inch centres only, and it is not permitted in an exterior bearing wall at all. Whether 24 works for you is also a question about what the finish will do, since drywall on 24 inch centres shows more.
Will drywall edges land on a stud at 16 or 24 inch centres?
Both, always, and that is not luck. A 48 inch sheet is exactly three bays at 16 inches or two at 24, because the 16 inch module and the 4 foot sheet are the same system by design. It is the one place American framing is easier than metric: a 1200mm board divides by 400 and 600 centres and does not divide by 450 or 500, which is a real trap in the UK and a non-issue here.
How many studs do I need for a 3.6m wall at 600 centres?
Seven, not six. Length divided by centres gives six, and six is the number of gaps. Studs are fence posts, not fence panels: one at each end and five in between. Every calculator that returns length over centres is one stud short on every wall.
Should studs be at 400 or 600 centres?
Both work with a 1200mm plasterboard, which is what matters for the boarding: 400 gives three bays per board, 600 gives two. 400 is stiffer and gives more fixing; 600 uses less timber. What it needs structurally is a design question and not one this tool answers.
Why does the board width have to divide by the centres?
Because a board edge must land on the centre of a stud to have something to fix to. If it floats between studs the joint has no support behind it and it cracks. 1200 divides by both 400 and 600. It does not divide by 450 or 500, which people occasionally use, and the tool will say so.
How many noggins do I need?
One per bay per row. A 3.6m wall at 600 centres has six bays, so six noggins in a single row. Over about 2.4m high, two rows is usual: both to stiffen the studs and to give a fixing wherever boards break horizontally.
How long should the noggins be cut?
The clear gap between studs, which is the centres minus the thickness of a stud: 562mm for 600 centres and 38mm studs, not 600. It sounds obvious written down and it is a very easy thing to cut a whole pack of wrong.
Does it work out the header over a doorway?
No. It allows two extra studs per opening for a trimmer each side, which is a working allowance. What the head itself needs depends on what is above it and whether the wall carries anything, and that is a design decision this site does not make.