Plywood Calculator

Plywood Sheathing Is Ordered by the Sheet, Sized by the Job

Subfloors, roof decking, and wall sheathing all use the same standard 4 ft × 8 ft plywood sheet, but the number of sheets a job needs depends entirely on the area being covered and how much gets trimmed away at the edges. This calculator turns a floor or wall area into a sheet count using the actual sheet size your supplier stocks.

The Formula

Area is entered directly, or built from length times width if you don't already have a total. The calculator applies a waste allowance — 10% by default — for trim and cuts, then divides by the sheet size, defaulting to 32 sq ft for a standard 4 ft × 8 ft sheet (2.97 m² for a standard 1.22 m × 2.44 m metric sheet), and rounds up since a partial sheet still requires buying a whole one.

Where This Calculation Matters

• Subfloor installation — tongue-and-groove subfloor sheets are laid with staggered seams, which increases trim waste slightly above a simple straight-edge layout.
• Roof decking — sheathing a roof uses the same sheet-count math as a floor, applied to the sloped roof area rather than the flat footprint.
• Non-standard sheet sizes — thicker sheathing, subfloor-specific products, or specialty panels sometimes come in different sheet dimensions, which is why the sheet size is an adjustable input rather than fixed.

Worked Example

A 12 ft × 16 ft floor (192 sq ft), using standard 32 sq ft sheets and the default 10% waste allowance:

How to Use This Calculator

1. Select Feet (sq ft) or Meters (sq m).
2. Enter the Length and Width of the area to cover.
3. Optionally adjust the Sheet Size — defaults to 32 sq ft (a standard 4 ft × 8 ft sheet).
4. Optionally adjust the Waste % — defaults to 10%.
5. Select Calculate to see the number of sheets needed.

Related Calculations

Framing the structure the plywood attaches to? The Lumber Calculator covers joists and framing stock, and the Roofing Calculator handles the shingle layer that goes over roof decking.