Start With a Plan or Sketch
It’s easiest to do a takeoff when you’re working from a set of construction plans or at least from a rough sketch of the wall frame. If you don’t have construction drawings, start by creating a sketch of the wall to identify the overall length and height of the wall and the size of all door and window openings. Determine the “on-center” spacing of the wall studs: the distance between the centers of neighboring studs. Standard stud spacing is 16 inches on-center. Also, note any corners in the wall or places where the wall intersects with other walls.
Estimate the Plates
Standard frames for load-bearing walls include a single bottom plate and two top plates. To calculate the linear feet needed for the plates, multiply the total length of the wall times 3, then add 5 to 10 percent for waste. For example, if the wall is 20 feet long, you would need 60 linear feet of plate lumber plus 1 to 2 feet for waste. Depending on the length of the wall, you may decide to use single, full-length pieces for each plate. If the wall will stand on a concrete floor or foundation, the bottom plate must be made of pressure-treated lumber.
Calculate the Studs
Determine the number of studs needed by starting with a quick calculation for the general studs and adding studs for specific elements:
Determine the Header Material
Headers for standard-size doors and windows often are built with two pieces of 2x12 lumber sandwiched over a piece of 1/2-inch-thick plywood cut to the same size as the header. The total thickness of the header is 3 1/2 inches to match the width, or depth, of a 2x4 wall frame. To estimate the framing materials for each window and door opening, use the total width of the opening plus 7 inches. For example, for a 36-inch wide door, you need two pieces of 2x12 at 43 inches and one piece of plywood at 11 1/4 inches (the actual width of a 2x12) by 43 inches.
Add Extras
Add extra stud material for fire blocking, structural connections, window sills, temporary bracing, and other additional elements, as needed.
Estimate Sheathing
To calculate the number of 4-by-8-foot sheets of sheathing needed for a wall frame, determine the area of the wall, then convert that value to the number of sheets: For example, if the wall is 8 feet tall and 20 feet long, it has a total area of 160 square feet. If there is a 4-by-5-foot window opening, the total area to cover is 160 - 20 = 140. Divide 140 by 32 to get 4.375. Round up to 5. This wall requires five 4-by-8-foot sheets of sheathing.
