Plywood and OSB sheathing are sold by the sheet, and in North America the standard panel is 4 × 8 ft, or 32 ft². Counting sheets starts with the area to cover divided by 32, plus a waste allowance for cuts at edges, openings, hips and valleys. Walls 9 or 10 ft tall are often sheathed with 4 × 9 or 4 × 10 panels, which run from the sill to the top plate in one piece. Roofs need the sloped area, not the footprint. This plywood calculator handles floors, walls (with openings subtracted) and roofs (with a pitch factor), in imperial or metric panel sizes, and also estimates cost and the weight you'll be hauling.
Roofing over the sheathing? The roofing shingles calculator counts shingle bundles on the same roof. For interior wall board, use the drywall calculator.
How to use the plywood & osb sheathing calculator
- Choose floor, walls or roof.
- Floor: enter the area. Walls: enter the total wall length and height, and subtract large openings. Roof: enter the footprint including overhangs and the pitch.
- Choose the panel size. For walls taller than 8 ft, 4 × 9 or 4 × 10 panels avoid horizontal joints.
- Use 10% waste for simple shapes and 15% or more for complex roofs, many openings or diagonal layouts.
- Optionally enter the price and the weight per sheet from the label.
Formula
A 4 × 8 sheet covers 32 ft²; 1220 × 2440 mm covers 2.98 m² (32.0 ft²). The calculator uses the face area of the panel. Leave the recommended gaps between panels: APA – The Engineered Wood Association recommends 1/8-inch spacing at panel edges and ends to prevent buckling as the panels take on moisture.
Worked example
A 40 × 28 ft roof footprint (including overhangs) at 6/12 pitch, in 4 × 8 sheets with 10% waste.
- Footprint: 1,120 ft². Pitch factor: 1.1180.
- Roof area: 1,120 × 1.118 = 1,252 ft².
- Exact sheets: 1,252 ÷ 32 = 39.1.
- With 10%: 43.0, so 44 sheets.
Walls: 120 ft of 8 ft walls is 960 ft². Minus 120 ft² of openings, that leaves 840 ft², or 26.25 sheets, and 29 with 10% waste. Many framers subtract only large openings such as garage doors, because the cut-outs from window openings are rarely reusable.
Sheets per area
| Area | 4 × 8 sheets (exact) | With 10% |
|---|---|---|
| 100 ft² | 3.1 | 4 |
| 250 ft² | 7.8 | 9 |
| 500 ft² | 15.6 | 18 |
| 1,000 ft² | 31.3 | 35 |
| 1,500 ft² | 46.9 | 52 |
| 2,000 ft² | 62.5 | 69 |
Choosing the panel
Structural plywood and OSB are rated for roof, wall or floor use by span rating, for example 24/16, meaning the panel can span 24 in between roof supports or 16 in between floor supports. Thickness and span rating must suit your framing spacing and loads under your building code, so check the APA stamp. Install panels with the long dimension (the strength axis) across the supports unless the rating allows otherwise, and stagger the end joints. APA publishes load-span tables and installation guides. For floors, tongue-and-groove sheathing rated for floors is glued and fastened to the joists per the manufacturer's schedule. The weight of a sheet varies with thickness, species and moisture, so read it from the label or supplier.
Caveats and assumptions
- Gable-end triangles on walls aren’t included; add their area (½ × base × height) separately.
- Roofs with several pitches should be calculated per section.
- The waste allowance covers cuts; complex layouts can need more.
- Panel thickness, span rating and fastening must meet local code; this tool only counts sheets.
Frequently asked questions
How many sheets of plywood do I need?
Divide the area by 32 ft² for 4 × 8 sheets and add about 10% for waste. 1,000 ft² needs 31.3 sheets exactly, or 35 with waste.
How many sheets of plywood for a 24 × 24 floor?
576 ft² ÷ 32 = 18 sheets exactly, or 20 with 10% waste.
How much does a 4 × 8 sheet cover?
32 square feet, or about 2.97 m². A metric 1220 × 2440 mm sheet covers 2.98 m².
Should I subtract windows when sheathing walls?
Subtract large openings like garage doors. Many framers sheathe over smaller window openings and cut them out, since the scraps are rarely reusable.
What gap should I leave between plywood sheets?
APA recommends 1/8-inch spacing at panel edges and ends to prevent buckling, unless the manufacturer says otherwise.
Sources
- APA – The Engineered Wood Association — Plywood — panel properties, strength axis, load-span tables, 1/8 in spacing
- U.S. Department of Commerce / NIST — Voluntary Product Standard PS 1 (Structural Plywood) and PS 2 — span-rated structural panels
- NIST SP 811, Appendix B — conversion factors — square feet to square meters
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.