Plywood Sheathing Calculator

Estimate plywood or OSB sheathing sheets needed for roof or wall framing from total area, sheet size, and waste factor.

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Result

42 sheets

Plywood sheathing sheets needed (incl. 10% waste).

Total area with waste
1,320 sq ft
Roof area
1,200 sq ft
Sheet area
32 sq ft

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Structural Sheathing

Estimating plywood or OSB sheathing sheets

A plywood sheathing calculator estimates the number of 4-by-8 sheets needed for roof decking or wall sheathing from total area and a waste allowance. This guide covers sheet sizing, staggered layout, and the difference between plywood and OSB.

Sheet count from area

A standard sheet of plywood or OSB is 4 feet by 8 feet, covering 32 square feet. Divide the total sheathing area by 32 and add a waste factor of 5 to 10 percent for cuts and fitting around openings, hips, and valleys.

Roof sheathing should be installed with staggered joints so that no four panel corners meet at a single point. This staggering may slightly increase waste on the first and last rows.

Sheets = ceil(Total area / 32 x (1 + Waste %))

Round up because partial sheets still require a full sheet purchase.

Plywood vs OSB

Both plywood and OSB are rated for structural sheathing when stamped with the appropriate span rating. Plywood is more moisture-tolerant at edges, while OSB is more dimensionally consistent across the sheet. Local codes and manufacturer warranties may favor one over the other.

Frequently asked questions

What thickness of plywood is used for roof sheathing?

The most common roof sheathing thickness is 7/16-inch for OSB or 15/32-inch (half-inch nominal) for plywood, though rafter spacing wider than 16 inches on center may require thicker panels.

 How much waste should I add for a hip roof?

Hip roofs produce more triangular cuts, so a 10 to 15 percent waste factor is recommended compared to 5 percent for a simple gable roof.

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