Last updated: 2026-07-02

Plywood Sheathing

Plywood and OSB sheathing are sold by the sheet, and the number a project needs comes down to two things: the area to cover and the footprint of a single sheet. This calculator estimates how many sheets are required to sheath a wall, roof plane, or subfloor, including a waste allowance for cuts and offcuts, and an optional cost estimate from the price per sheet.

Area, sheet coverage, and waste

Start by measuring the area to sheath. For a rectangle this is length times width; for an irregular surface, split it into rectangles and add the pieces together. Next, find the coverage of one sheet from its length and width:

where $L$ and $W$ are the sheet dimensions. A standard sheet is 4 ft by 8 ft, which covers 32 ft² (about 2.97 m²). Dividing the surface area by this coverage gives the number of sheets for a perfect, cut-free fit. Real work always needs a few extra for the pieces cut around openings and edges, for offcuts too small to reuse, and for spares. A waste allowance expands the count, which is then rounded up to a whole sheet:

where $A$ is the surface area and $k$ is the waste allowance as a fraction. Rounding up matters because a partial sheet cannot be bought, and running short mid-project usually means an extra trip to the supplier.

If a price per sheet $p$ is entered, the material cost follows directly:

Worked example

Choosing inputs

Use the actual sheet dimensions your supplier stocks; the common size is 4 ft by 8 ft, but 4 ft by 9 ft and 4 ft by 10 ft sheets exist for taller walls. Pick a larger waste allowance for roofs with hips and valleys, for walls with many windows and doors, and where the framing layout forces small offcuts. The count is the same for plywood and OSB of equal size, so choose the panel material on cost, weight, and moisture behaviour rather than on how many sheets cover the surface. For structural framing lumber measured by volume, see Board Foot Calculator.