Use this sheathing calculator to estimate how many OSB or plywood sheets you need for a wall, roof, floor, gable end, or general sheathing area. It is a material planning tool, not a code, fastening, span, wind, or structural design calculator.
The count changes with surface shape, openings, panel size, waste, roof pitch, and how many separate sections you are covering. Always verify the final quantity against the framing layout, panel direction, required spacing, local code, and the panel manufacturer’s installation instructions.
Estimate your sheathing sheets
Only applies when using roof footprint mode.
How this estimate works
The calculator estimates gross area, subtracts large openings, adds a waste allowance, divides by panel coverage, and adds optional extra sheets for field cuts or repair uncertainty. The default panel is a 4 × 8 sheet with 32 square feet of coverage.
When to use the different modes
- Use rectangle mode for walls, roof planes, floors, and simple sheathing areas.
- Use gable mode for triangular gable-end sheathing.
- Use roof footprint mode only for a rough roof estimate when actual roof plane area is not known.
- Use total area mode when you already measured the square footage separately.
What this calculator does not decide
This calculator does not choose panel thickness, span rating, exposure rating, fastening schedule, nail spacing, braced wall method, roof diaphragm design, or structural repair scope. Those depend on the building, code, manufacturer instructions, and sometimes engineering.
Do not order exactly the base sheet count
The base count assumes every offcut is usable. Real sheathing work has corners, openings, staggered seams, panel spacing, roof edges, cutouts, damaged sheets, and mistakes. A normal waste allowance is safer than trying to buy the exact mathematical count.