How to use the wall framing calculator
- Enter the wall length and height. Height runs from the floor to the top of the double top plate. Use
20'or8' 1 1/8. - Pick the stud spacing. 16" O.C. is standard for exterior and bearing walls. 24" works for many non-bearing walls where code allows it.
- Count corners, intersections and openings. Count each corner on only one of the two walls that meet there, or you'll buy the extra studs twice.
- Pick your plate length. Longer boards mean fewer splices in the plates.
The math
Stud length is the wall height minus three plates (one bottom, two top) at 1½" each. A wall 8' 1⅛" tall takes 97⅛ − 4½ = 92⅝" studs. That's why lumber yards sell 92⅝" precut studs: with a double top plate they make an 8' 1⅛" wall, which leaves room for 8' drywall plus a ceiling.
Layout studs are the wall length divided by the spacing, rounded down, plus one, plus one more if there's a leftover gap at the end. That's the same count as the stud layout calculator. Then the extras:
- Corners: 2 extra studs, so the corner has a nailing surface for drywall on both sides.
- Wall intersections: 2 extra studs for backing where a partition wall tees in.
- Doors and windows: 2 extra studs for the jacks. The king studs and cripples come from the layout studs the opening replaces.
Plates: each of the three plate rows needs the wall length in boards. Sheathing: wall area ÷ 32 sq ft per 4×8 sheet, with no deduction for openings, since the cutouts rarely make usable pieces.
Example: a 20' wall, 8' 1⅛" tall, 16" O.C., with 2 corners, 1 intersection and 2 openings. Layout studs: 240 ÷ 16 = 15 bays + 1 = 16. Extras: 2 × (2 + 1 + 2) = 10. With 10% waste, 26 × 1.1 = 28.6, so 29 studs of 92⅝" precut. Plates: 16' boards, 2 per row, so 2 for the bottom and 4 for the top. Sheathing: 20 × 8.09 = 161.9 sq ft, plus 10% = 178 sq ft ÷ 32 = 6 sheets.
Tips
- Stagger top plate splices. The IRC calls for end joints in the double top plate to be offset at least 24", and for the top plate to lap at corners and intersections. Plan your board lengths so splices don't line up.
- Treated bottom plate on concrete. The IRC (R317.1) calls for pressure-treated or naturally durable wood for framing on a foundation wall less than 8" above exposed ground, and for plates on a slab that sits on the ground without a moisture barrier. Most framers use treated plates on any concrete.
- Crown the studs. Sight down each stud and face the crowns the same way so the wall stays flat for drywall.
- Lay out before you nail. Tack the plates together and mark both at once so the studs land on the same marks top and bottom.
FAQ
How many studs do I need for a wall?
Divide the wall length in inches by the spacing (16 or 24), round down and add one, plus one more if there is a leftover gap. Then add 2 studs for each corner, each wall intersection and each door or window, and about 10% waste.
What length studs do I need for an 8 foot wall?
For a standard 8' 1⅛" wall with one bottom plate and a double top plate, use 92⅝" precut studs. Subtract 4½" (three 1½" plates) from the wall height to get the stud length for any wall.
How many plates does a wall need?
Most walls have a single bottom plate and a double top plate, so three rows of plate lumber the length of the wall. The IRC calls for a double top plate on wood stud walls, with splices offset at least 24". Interior non-bearing walls may use a single top plate.
How many sheets of sheathing do I need for a wall?
Multiply the wall length by its height in feet and divide by 32 for 4×8 sheets, then add about 10% for waste. Most framers don't subtract windows and doors, since the cutouts are rarely usable.