Formula
Layout studs are floor(length in inches ÷ spacing) + 1. They are marked across the whole wall. A stud that would have landed in an opening is not deleted here. The kings, jacks, and the cripples above and below the opening are the opening count, and they roughly replace it. Each opening adds 2 king studs and 2 jacks for each jack you set per side. A corner end adds 2 studs. A partition T adds 2 studs, or 1 if you choose a ladder.
studs = ceil((layout + openings + corners + T's) × (1 + waste ÷ 100))
stud length = wall height − 1.5 in × plate courses
header length = rough opening + 2 × 1.5 in × jacks per side
plates = courses × ceil(wall length ÷ stock length)
sheets = ceil(wall area ÷ sheet area × (1 + waste ÷ 100))
A 20 ft wall at 16 in is 16 layout studs. Both ends as corners add 4. Ten percent waste makes 22 studs at 92 5/8 in. Three plate courses, 20 ft each, are 60 ft, bought as 6 pieces of 16 ft stock. Sheathing is about 161.9 ft², which is 6 sheets of 4×8 after 10% waste. A rule of thumb of one stud per foot would have said 20 studs before waste. This count is the layout plus the corners.
A header is two plies of that length. The page will not say what those plies are. IRC Table R602.7 is the header table. R602 is the wood-wall chapter for stud size, spacing, and bracing. A 2×4 wall and a 2×6 wall both dress to about 1½ inches of plate thickness under the American Softwood Lumber Standard PS 20. Sheathing panel sizes 4×8, 4×9, and 4×10 are the APA panel sizes. This page does not cover point loads, shear walls, hold-downs, fire blocking, or the energy code.
Worked examples
20 ft, 16 in, 97⅛ in tall, both ends corners, 10% waste, 16 ft plates, 4×8 at 10%. 16 layout studs, 4 corner studs, 22 studs at 92 5/8 in. 6 plate pieces, 60 ft. 6 sheets.
12 ft, 24 in, one 36 in door and one 48 in window, one jack per side, no corners, no waste. 7 layout studs, 8 opening studs, 15 studs. Headers 39 in and 51 in, two plies each.
30 ft, 16 in, no extras, no waste. 23 studs.
96 in wall, double top plate. Stud cut length 91.5 in.
72 in rough opening, two jacks per side. Header 78 in, two plies. Opening studs: 6.
Reference
The 20 ft precut wall above is the default. Header length is a cut length. It is not a size.
| Piece | Count | Length |
|---|---|---|
| Stud | 22 | 92 5/8 in |
| Plate | 6 | 16 ft stock |
| Sheathing | 6 | 4 × 8 |
Questions
How many studs for a 20 ft wall?
At 16 inches on center, floor(240 ÷ 16) + 1 is 16 layout studs. Two three-stud corners add 4. With 10% waste that is 22 studs, cut to 92⅝ inches when the wall is 97⅛ inches tall with a single bottom plate and a double top plate.
How do I calculate studs at 16 inches on center?
Divide the wall length in inches by 16, drop the fraction, and add 1. That count runs the whole wall. This page does not remove the studs that land in a door or a window. Kings, jacks, and the cripples that replace those studs are counted with the opening.
How long is a stud for an 8 ft wall?
A wall that is exactly 96 inches, with a double top plate and a single bottom plate, needs a stud of 91½ inches. The common precut is 92⅝ inches, and it fits a wall of 97⅛ inches, which is what lumber yards call an 8 ft wall.
How many studs are in a corner?
This page adds two extra studs for each end you mark as a corner, which is the three-stud corner. A ladder at a partition intersection adds one stud instead of two. A two-stud advanced-framing corner is a different assembly and is not what the corner count assumes.
What size header do I need?
It depends on the span, the load, and the snow. IRC Table R602.7, or an engineer, sizes the header. This calculator only gives the length: the rough opening plus 1½ inches for each jack on each side, and it lists two plies. It does not name a 2×6, a 2×8, or an LVL.
How many sheets of OSB for a wall?
Wall area divided by the sheet, times waste, rounded up. A 20 ft wall at 97⅛ inches is about 162 square feet. A 4×8 sheet is 32 square feet, so 10% waste rounds to 6 sheets. Openings are left in the area unless you turn subtraction on. Round up on each wall.
Should the wall be 2×4 or 2×6?
This page does not choose. Energy code, a plumbing wall, and the loads on the wall are outside a piece count. Plate thickness is taken as 1½ inches either way, from the dressed size in PS 20.
Sources
- International Code Council, IRC Chapter 6, R602 wood wall framing, and Table R602.7 for headers. Those sections are where stud size, spacing, and header size are decided. This page does not apply the table. Local amendments govern.
- American Softwood Lumber Standard PS 20. A nominal 2 inch board dresses to 1½ inches. Plate thickness on this page is that 1½ inches.
- APA – The Engineered Wood Association publishes structural wood panels in 4×8, 4×9, and 4×10. Sheet count here is area divided by 32, 36, or 40 square feet, plus waste, rounded up per wall.
- Precut studs of 92⅝ inches match a 97⅛ inch wall with one bottom plate and two top plates. A wall that is exactly 96 inches needs a 91½ inch stud. Drywall on the same wall is the drywall calculator.