How to Calculate Plywood Requirements
Coverage area divided by sheet size, with layout waste added
Sheet coverage
A standard plywood sheet is 4 ft × 8 ft, covering 32 square feet. Divide the total area you need to cover (a subfloor, wall sheathing, or roof deck) by 32 to get the base number of sheets, before any waste allowance.
Layout waste
Real layouts rarely use every sheet perfectly — sheets get cut to fit around framing irregularities, openings, and the edges of a floor or roof plane. A waste allowance in the range of 10-15% is common, higher for complex or irregular layouts (multiple roof planes, many penetrations).
Sheet thickness depends on application, not on this calculation
Board count from area covers how many sheets you need — it says nothing about what thickness to use. Subfloor, wall sheathing and roof decking each have their own thickness and span-rating requirements set by the framing spacing and application, which should come from the structural design or local code, not from a coverage calculation.
Worked Example
A 960 ft² subfloor, standard 4×8 sheets, 10% waste.
Base sheets: 960 ÷ 32 = 30 sheets
With 10% waste: 30 × 1.10 = 33 sheets