Wall sheathing calculator: OSB or plywood for exterior walls
Enter the wall perimeter and height, the windows and doors you want to deduct, and any gable ends. The calculator counts 4×8, 4×9, 4×10 or metric sheathing panels with waste and cost.
Walls 960.0 sq ft − openings 160.8 sq ft = 799.2 sq ft
You need 28 sheets of 4×8 ft (48 × 96 in) (24.98 before 10% waste)
Worked examples
| Job | Area | Panel | Waste | Sheets |
|---|---|---|---|---|
| 24 × 36 ft house, 8 ft walls, 10 windows, 2 doors | 799.2 sq ft | 4×8 ft (48 × 96 in) | 10% | 28 |
| Same house with 9 ft walls on 4×9 sheets | 919.2 sq ft | 4×9 ft (48 × 108 in) | 10% | 29 |
| 24 × 24 ft garage, 9 ft walls, 16 × 7 door, 2 gables at 6/12 | 887.0 sq ft | 4×9 ft (48 × 108 in) | 10% | 28 |
| 12 × 16 ft shed, 8 ft walls, 2 gables at 4/12, no deductions | 472.0 sq ft | 4×8 ft (48 × 96 in) | 10% | 17 |
| 10 × 8 m house, 2.6 m walls, 8 windows 1.2 × 1.2 m, 2440 × 1220 mm | 78.3 m² | 2440 × 1220 mm | 10% | 29 |
How wall sheathing is estimated
Add up the length of every exterior wall (the perimeter of a rectangular house is 2 × length + 2 × width) and multiply by the wall height to get the gross wall area. Add the triangular gable ends if the walls under a gable roof are sheathed up to the rafters: each triangle is width × rise ÷ 2, where the rise is half the width times the pitch (a 24-ft gable at 6/12 rises 6 ft, so it is 72 sq ft). Then subtract windows and doors, add waste and divide by the panel area.
Should you subtract windows and doors?
Framers often sheathe straight over small windows and cut the openings out afterwards with a router or saw, because it is faster and keeps panel joints off the corners of openings, where cracks start. The offcuts from openings are rarely big enough to reuse on the wall. A safe estimate deducts only large openings — garage doors, patio doors and window walls — and ignores small windows. If you deduct every opening, keep the waste allowance at 10% or more. Enter 0 windows in the calculator to see the no-deduction number for comparison.
Pick the panel to match the wall height
| Wall height | Panel | Why |
|---|---|---|
| 8 ft (8 ft 1 1/8 in plate height) | 4×8 vertical | One sheet covers bottom plate to top plates with no horizontal joint. |
| 9 ft | 4×9 vertical | Covers the wall plus part of the rim joist or band, tying floors together. |
| 10 ft | 4×10 vertical | Avoids a horizontal seam that would need blocking on shear walls. |
| 2.4–2.7 m (metric) | 2440 × 1220 or 2700 × 1200 mm | Same idea: choose a panel at least as tall as the wall. |
Taller panels cost more per sheet but cut labor and blocking. When the wall is taller than the panel, sheets laid horizontally (long edge across the studs) are stronger in bending, but seams between rows must be blocked if the wall is a braced or shear wall.
Installation notes
- 7/16-inch OSB is the most common wall sheathing in North America; 15/32 or 1/2-inch plywood and integrated-barrier panels are used where higher shear values or better moisture tolerance are wanted.
- Start at a corner with a full sheet plumb on the stud layout so every vertical edge lands on a stud center (16 or 24 in on center).
- Leave a 1/8-inch gap between panels and nail on the schedule for your wall — commonly 6 in at panel edges and 12 in into intermediate studs; shear walls often need a tighter pattern.
- Do not let a vertical joint line up with the edge of a window or door; let the sheet run past the corner of the opening and cut it out.
How to use the calculator
- Measure the walls. Add the length of every exterior wall and measure the wall height from the bottom of the plate to the top of the top plates.
- Add gable ends. Enter the number of gable triangles to sheathe, their width and the roof pitch.
- Deduct big openings. Enter windows and doors to subtract — usually only the large ones.
- Choose panel and waste. Pick a panel at least as tall as the wall, set 10% waste and read the sheet count.
Other plywood calculators
- Subfloor calculatorFloor area → 4×8 or 2440 × 1220 subfloor panels
- Roof sheathing calculatorFootprint, overhang and pitch → roof deck sheets
- Kitchen cabinetsSheets per base and wall cabinet
- BookshelvesSheets by bookcase height and width
Cutting parts rather than laying whole sheets? Area estimates undercount furniture and cabinets — use the cut list optimizer, and see plywood sizes and thicknesses for real panel dimensions.
FAQ
How many sheets of OSB do I need for an 8 ft wall?
Divide the wall length by 4 ft and round up — each vertical 4×8 sheet covers 4 ft of an 8-ft wall. A 120-ft perimeter with 8-ft walls is 960 sq ft, or 30 sheets before deducting openings and adding waste.
How do I calculate sheathing for a gable end?
A gable is a triangle: width × rise ÷ 2. The rise is half the width times the pitch, so a 24-ft gable at 6/12 rises 6 ft and covers 72 sq ft — 2.25 sheets plus waste. Expect more waste than on a rectangular wall because of the sloped cuts.
Should wall sheathing go vertical or horizontal?
Either is allowed. Vertical is most common because every edge lands on a stud and one sheet covers an 8-ft wall. Horizontal is stiffer across the studs, but on braced or shear walls the horizontal seam must be blocked.
Do I subtract windows when ordering sheathing?
Usually only large openings such as garage and patio doors. Small window openings are often sheathed over and cut out, and their offcuts are seldom reusable.