How it works
The calculator lays the studs out along the wall at the spacing you enter, adds the studs for corners and openings, and counts the plate boards for the number of plate rows.
Layout studs = ⌈ Wall length ÷ Spacing ⌉ + 1
Extra studs = Corners × Studs per corner + Openings × Studs per opening
Studs = ⌈ (Layout studs + Extra studs) × (1 + Extra ÷ 100) ⌉
Plate length = Plate rows × Wall length
Plate boards = ⌈ Boards for the plate rows × (1 + Extra ÷ 100) ⌉
⌈ ⌉ means rounding up. The layout always has one more stud than it has spaces, because the wall needs a stud at both ends. For the plates, a row no longer than a board is cut from one board (two short rows can share a board); a longer row takes whole boards plus one cut piece, and cut pieces come out of further boards only as many times as they fit.
Worked example in words
A 20 ft wall with studs 16 in on center is 240 in long, which is 240 ÷ 16 = 15 spaces, so 16 studs on the layout. Two corners at 2 extra studs each and one window at 4 extra studs add 8, for 24 studs. With three plate rows the plates are 3 × 20 = 60 ft. Each 20 ft row takes one 16 ft board and a 4 ft piece; four 4 ft pieces come out of one board, so the three rows need four 16 ft boards.
What decides the spacing and the plates
The calculator does not choose a stud spacing. In the International Residential Code the size, height and spacing of studs follow Table R602.3(5): the maximum spacing ranges from 24 in down to 16 or 12 in depending on the stud size and on how many floors and roofs the wall carries (Seattle Residential Code 2015, Chapter 6, which adopts the 2015 IRC). Your plans or local code may call for something else, and walls with large openings, tall walls or heavy loads may need an engineer.
The same chapter says wood stud walls are capped with a double top plate, with end joints offset at least 24 in, and that studs bear on a bottom plate at least as wide as the studs. That is why three plate rows are filled in. If your plans use a single top plate under the code’s exception, change the plate rows to 2.
Corners, openings and lumber lengths
Corners, intersections and openings are framed in different ways, so the number of studs each one takes is yours to enter. Headers, sills, cripple studs and blocking are separate pieces and are not counted. Southern Pine dimension lumber is specified in standard lengths from 8 to 20 ft in two-foot steps (Southern Forest Products Association); pick the plate length you can buy, and choose stud lengths from your wall height after deducting the plates. In metric, enter your stud spacing in millimetres and the board length your supplier stocks – none is filled in.
This is a count of lumber, not a structural design. Stud size, spacing, headers and bracing must follow your plans and local code; have a qualified professional check anything you are unsure about.
Worked example
Inputs
- Wall length
- 20 ft
- Stud spacing (on center)
- 16 in
- Corners and wall intersections
- 2
- Extra studs per corner
- 2
- Doors and windows
- 1
- Extra studs per opening
- 4
- Plate rows
- 3
- Plate board length
- 16 ft
- Extra lumber
- 0 %
Result
- Studs on the layout
- 16
- Extra studs (corners, openings)
- 8
- Studs
- 24
- Plate length
- 60 ft
- Plate boards
- 4
Common mistakes
- Dividing the wall length by the spacing and stopping there. A wall needs one more stud than it has spaces, because there is a stud at both ends.
- Forgetting the extra studs at corners, wall intersections, doors and windows. They often add more studs than you expect – count them from your framing detail.
- Counting only one top plate. Most walls under the IRC get a double top plate, which makes three rows of plates in total.
- Choosing a stud spacing to save lumber. The spacing depends on the stud size, the loads and the sheathing, and is set by the plans, the code or an engineer.
- Buying plates at the exact length with no allowance for joint offsets. Top-plate joints have to be staggered, which can leave offcuts that cannot be used.
Assumptions and limits
- Studs are laid out at the spacing you enter from one end of the wall, with a stud at both ends; the number of spaces is rounded up.
- Extra studs are your own figure per corner and per opening. Headers, sills, cripple studs, blocking and fire blocking are not counted.
- Plates run the full wall length in every row. A row longer than a board takes whole boards plus one cut piece, and cut pieces are reused across rows only where they fit.
- Studs are counted, not sized – choose the stud length from the wall height and the plates you use.
- This is a lumber count, not a structural design. It does not check stud size, height, spacing, loads, headers or bracing.
Frequently asked questions
How many studs do I need for a wall?
Divide the wall length by the stud spacing, round up and add one for the stud at the far end. A 20 ft wall at 16 in on center has 240 ÷ 16 = 15 spaces, so 16 studs on the layout. Then add the extra studs your corners, intersections, doors and windows take.
Should studs be 16 or 24 inches on center?
That is a design decision, not something this calculator can choose. The IRC lists maximum stud spacing in Table R602.3(5) depending on stud size, height and what the wall carries, and your plans or local code may require less. Enter the spacing from your plans.
How many plates does a wall need?
Under the IRC, wood stud walls sit on a bottom plate and are capped with a double top plate, which is three rows. A single top plate is allowed only as an exception with specific ties at joints and corners, so follow your plans.
How many studs does a corner or a window take?
It depends on the framing detail – the type of corner, how intersecting walls are backed, and the king and jack studs at each opening. Enter the number of extra studs from your detail; the calculator multiplies it by the number of corners and openings.
How many plate boards should I buy?
The calculator multiplies the wall length by the number of plate rows and fits the runs onto the board length you enter. For a 20 ft wall with three rows and 16 ft boards, each row needs one full board and a 4 ft piece, and four 4 ft pieces come out of one board, so four boards in total.
Sources
- Seattle Residential Code 2015, Chapter 6 – Wall Construction (2015 IRC with amendments) — City of Seattle, Department of Construction and Inspections. R602.3.1: stud size, height and spacing follow Table R602.3(5) (maximum 12–24 in by stud size and load); R602.3.2: walls are capped with a double top plate, end joints offset at least 24 in; R602.3.4: studs bear on a bottom (sole) plate.
- Specifying Southern Pine Lumber – Specification Guidelines — Southern Forest Products Association. Dimension lumber is specified in standard lengths from 8 to 20 ft in two-foot increments.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 4, 2026