Stud calculator
Add your walls and the widths of the doors and windows. You get the studs, with the king and jack studs each opening needs, the header size for each opening from the IRC table, the plates, the stud length to buy, and a check of your stud size and spacing against the code.
Inputs
Result
| Opening | Header | Studs |
|---|
| Wall | Studs | Plate boards |
|---|
How it is worked out
A 20 ft wall with studs at 16 in on centre takes 240 / 16 = 15 spaces, so 16 studs. A 3 ft window in a one-storey wall 24 ft wide gets a 2-2x4 header with one jack stud and one king stud each side: 4 more, 20 in all. With 10% extra, buy 22. The plates are three rows of 20 ft: 60 ft, or six 16 ft boards.
The rule of thumb of one stud per foot of wall at 16 in on centre works because the extras at corners, openings and waste roughly make up the difference; the calculator counts them properly.
What the extras are
- Corners: a corner needs something to nail the drywall to on the inside. A traditional three-stud corner takes 2 studs beyond the end studs; a two-stud corner with drywall clips takes fewer.
- Intersections: where an interior wall meets another wall, 2 backing studs or ladder blocking catch both sides of the drywall.
- Doors and windows: each side of an opening has full-height king studs and one or more jack (trimmer) studs under the header. IRC Table R602.7(1) gives the jacks, 1 to 4 per end, with the header size, and Table R602.7.5 the king studs in exterior walls, 1 to 4 per end by the opening width and the design wind speed. The layout studs that land in the opening are cut into cripples above and below it, so they are still needed.
Header sizes
For exterior bearing walls the calculator picks the smallest header in IRC Table R602.7(1) that spans the opening, for what the wall carries, the ground snow load and the building width, and gives its length: the opening plus 1-1/2 in for each jack stud at each end. The table is for No. 2 Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir, with the top of the header braced by the framing above. The header size calculator shows every option. Sills and blocking are not counted.
Stud length
Precut studs are 92-5/8, 104-5/8 and 116-5/8 in. On a bottom plate and a double top plate, 4-1/2 in in all, they make walls of 97-1/8, 109-1/8 and 121-1/8 in: room for a 5/8 in drywall ceiling and a sheet of drywall held off the floor. For any other height, the stud is the wall height less the plates.
Stud size and spacing
IRC Table R602.3(5) sets the largest spacing by what the wall carries, and the calculator checks your choice against it:
| Studs | Roof and ceiling only | One floor + roof | Two floors + roof | Nonbearing |
|---|---|---|---|---|
| 2x3 | — | — | — | 16 in, 10 ft |
| 2x4 | 24 in | 16 in | — | 24 in, 14 ft |
| 3x4 | 24 in | 24 in | 16 in | 24 in, 14 ft |
| 2x5 | 24 in | 24 in | — | 24 in, 16 ft |
| 2x6 | 24 in | 24 in | 16 in | 24 in, 20 ft |
Bearing walls are limited to 10 ft between points of lateral support, unless they meet an exception in R602.3.1 or are designed. Exception 2 lets 2x6 No. 2 studs carrying a roof, with no more than 6 ft of roof bearing on them, go to 18 ft at 16 in on centre or 20 ft at 12 in, where the snow load is 25 psf or less and the design wind speed 130 mph or less; the calculator flags it. A dash means not permitted: 2x4 studs cannot carry two floors. 2x3 studs may not be used in exterior walls, and 2x4 studs under a habitable attic are limited to a 32 ft roof span. Your sheathing and drywall must also span the spacing.
Sheathing the walls? The plywood calculator counts the sheets. For drywall, the drywall calculator.
Questions
How many studs do I need for a wall?
Divide the wall length in inches by the spacing, round up and add one. Then add 2 for each corner, a king and the jack studs each side of every door or window, and about 10% for waste. A 20 ft wall at 16 in on centre with one window takes 20 studs, 22 with waste.
Can I use 2x4 studs at 24 inches on center?
In a bearing wall, only where it carries just a roof and ceiling, under IRC Table R602.3(5). With a floor above, 2x4 studs must be 16 in on centre, and they cannot carry two floors. Nonbearing 2x4 partitions can be 24 in.
How many jack studs does a header need?
IRC Table R602.7(1) gives it with the header size: one per end for short headers under light loads, up to four for wide openings under two floors and heavy snow.
How many studs do I need per foot of wall?
At 16 in on centre, about 0.75 per foot for the layout alone. With corners, openings and waste, estimators use one stud per linear foot as a quick check.
How long is a stud for an 8 ft wall?
92-5/8 in. On a bottom plate and a double top plate it makes a 97-1/8 in wall, which allows for a 5/8 in drywall ceiling.
How many studs for a 10 ft wall?
At 16 in on centre, 120 / 16 = 7.5 spaces, rounded up to 8, plus 1: 9 studs, before corners, openings and waste. At 24 in, 6.
How many studs are in a corner?
Usually three: the end stud of each wall plus one more, so 2 more than the end studs alone. Energy-efficient framing uses two studs and drywall clips.
Do I need a double top plate?
The IRC calls for a double top plate, with end joints offset at least 24 in. A single top plate is allowed where the rafters or joists sit over the studs and the joints at corners, intersections and splices are tied with galvanized steel plates; Table R602.3.2 gives a 3 x 6 in plate with six 8d nails each side at corners, and 3 x 12 in with twelve at butt joints, in most cases.
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