Plywood Calculator
This plywood calculator finds how many sheets of plywood or OSB you need to sheath a wall, floor, or roof. Enter the length and height or width, subtract windows and doors, pick the sheet size and waste allowance, and the plywood calculator returns the sheet count, the area, and the material cost.
Results
The Plywood Calculator is part of our Materials Estimating collection. Browse more materials estimating to size, convert, and check your work alongside this tool.
What the plywood calculator does
Sheathing is bought by the sheet, and a 4 × 8 ft sheet covers 32 square feet. The plywood calculator works out the area to cover, takes away openings such as windows and doors, adds a waste allowance for cuts, and divides by the sheet area, rounding up. It works the same for plywood and OSB on walls, subfloors, and roof decks.
Plywood square footage formula
Area, minus openings, plus waste, divided by sheet area:
A 4 × 9 sheet covers 36 sq ft and a 4 × 10 sheet 40 sq ft, handy for 9 and 10 ft walls so one sheet spans plate to plate.
Plywood calculator example
A 40 ft wall, 8 ft high, with 40 sq ft of windows and doors, 4 × 8 sheets, 10% waste:
At $35 a sheet that is $350. For a roof, enter each slope separately using the rafter length, not the building width.
How to use the plywood calculator
For a wall, enter its length and height in feet; for a floor, its length and width; for a roof, the length along the eave and the rafter length from eave to ridge for each slope. Enter the total area of windows and doors to subtract. Pick the sheet size, set a waste allowance of 10% or more for roofs and walls with many cuts, and add the price per sheet for a cost.
Reading how many sheets of plywood you need
The sheet count is rounded up, so you always have enough to finish. Many builders do not subtract small windows because the offcuts rarely fit elsewhere; subtract only large openings such as garage doors. Roofs with hips, valleys, and dormers waste more, so raise the allowance to 15% or more. Buy one or two spare sheets for damage on site.
When to use a sheathing calculator
- Ordering wall sheathing for a house or shed
- Pricing a roof deck replacement
- Counting subfloor sheets for an addition
- Comparing plywood and OSB costs
- Planning 9 or 10 ft walls with tall sheets
Common plywood calculator mistakes
- Using building width for a roof. Use the sloped rafter length.
- No waste allowance. Cuts around openings and gables use extra sheets.
- Subtracting every small window. Offcuts often cannot be reused.
- Wrong thickness. Check the panel span rating for your framing.
Tips for ordering sheets of plywood
- Order 1 or 2 extra sheets for damage.
- Use 4 × 9 or 4 × 10 sheets on tall walls.
- Keep sheets flat and dry until they go up.
Roof sheathing calculator tips
Roof area is larger than the floor below it because of the slope. Use the rafter length, including overhang, for the second dimension of each slope, or work it out from the span and pitch with the rafter length calculator. Lay sheets with the long edge across the rafters, stagger the joints, and leave about 1/8 in gaps between sheets for expansion, as many sheathing makers recommend. Use H-clips between rafters where the span calls for them. Roof thickness depends on rafter spacing and snow load; 7/16 in OSB or 1/2 in plywood is common on 24 in centers in many areas, but follow the panel span rating and local code.
Wall sheathing and subfloor calculator notes
Wall sheets usually run vertically, so a 9 ft wall with a 4 × 9 sheet needs no horizontal joint, saving blocking and labor. Subfloors use tongue and groove panels laid across the joists, glued and screwed, with the long edge perpendicular to the framing. Count studs for the same wall with the stud calculator, and get the roof area for shingles from the roofing calculator.
Plywood sheet calculator chart for 8 ft walls
4 × 8 sheets for an 8 ft wall with no openings and 10% waste:
| Wall length | Wall area | Sheets |
|---|---|---|
| 10 ft | 80 sq ft | 3 |
| 20 ft | 160 sq ft | 6 |
| 30 ft | 240 sq ft | 9 |
| 40 ft | 320 sq ft | 11 |
| 60 ft | 480 sq ft | 17 |
| 80 ft | 640 sq ft | 22 |
Plywood Calculator FAQ
How many sheets of plywood do I need?
Divide the area in square feet by 32 for 4 × 8 sheets, after adding about 10% for waste. A 280 sq ft wall needs 10 sheets.
How do I calculate roof sheathing?
Multiply the eave length by the rafter length for each slope, add them, add 10 to 15% waste, and divide by 32.
Should I subtract windows?
Subtract large openings. Small windows are often sheathed over and cut out, so many builders ignore them.
Is OSB the same size as plywood?
Yes. OSB comes in the same 4 × 8, 4 × 9, and 4 × 10 ft sheets, so the count is the same.