Quick answer: A standard 4x8 sheet of plywood or OSB covers 32 square feet. Divide your roof or wall area by 32 and add ~10% for waste to get the number of sheets.
This sheathing calculator finds how many 4x8 plywood or OSB sheets you need for roof or wall sheathing, plus fasteners and estimated cost, with a built-in waste factor.
Sheathing is the layer of structural panels — plywood or OSB — that covers your roof rafters or wall studs before the finish material goes on. Estimating it is simple: find your total area and divide by the coverage of one sheet.
The base requirement in the IRC is 8d common nails (0.131 in. diameter x 2-1/2 in. long), spaced 6 in. on center at supported panel edges and 12 in. on center at intermediate supports in the field of the panel. This is the 6/12 pattern. It is set out in IRC Table R602.3(1), and roof sheathing installation is covered by IRC R803.2.3.
| Requirement | Specification | Source |
|---|---|---|
| Nail type | 8d common, 0.131 in. x 2-1/2 in. | IRC Table R602.3(1); APA N335 |
| Panel edges bearing on framing | 6 in. on center | IRC Table R602.3(1) |
| Intermediate supports (field) | 12 in. on center | IRC Table R602.3(1) |
| Minimum distance from panel edge | 3/8 in. | APA N335 |
| Gap between panel ends and edges | 1/8 in. | APA N335 |
Box nails and sinkers are not a substitute. A box nail of the same length has a smaller shank diameter and lower withdrawal capacity. A spec that calls for 8d common is not satisfied by an 8d box.
Drive nails flush, not through. An overdriven nail that breaks the panel face loses a large share of its holding power. It is the most common sheathing defect inspectors write up.
High-wind and coastal zones require more. Many hurricane-prone jurisdictions amend the base code to a tighter pattern. A 4 in. edge and 8 in. field spacing is a common upgrade in coastal Florida, the Carolinas and Texas, and ring-shank nails are frequently mandated. These are local amendments rather than the base IRC, so confirm the required pattern with your building department before you sheathe.
The figures above are model-code minimums. Your local authority having jurisdiction may require more, and an engineered design always governs over the prescriptive table.
Is 15/32 in. the same as 1/2 in.? Yes. 15/32 in. is the actual manufactured thickness of the panel most people call half-inch sheathing. The 1/2 in. figure is a nominal call-out; a performance-rated panel is stamped with its real thickness. They are the same product, and a plan specifying 1/2 in. sheathing is satisfied by a 15/32 in. panel.
What does Structural 1 mean? Structural 1 (often stamped STRUCT 1) is a panel grade, not a thickness. It carries stricter veneer and species requirements and higher published shear values, which is why it gets specified for shear walls and diaphragms. A 15/32 in. Structural 1 panel is the same thickness as ordinary 15/32 in. sheathing, but rated for more load.
OSB or plywood for roof decking? Both are wood structural panels and both meet code at the same span rating and thickness. OSB is usually cheaper and more dimensionally consistent. Plywood dries faster after it gets wet and tends to hold edge fasteners a little better. Either way it is the span rating stamped on the panel, not the material, that has to match your rafter or truss spacing.
A 4 × 8 sheet covers 32 sq ft, so divide your wall or roof area by 32. Add about 10% for cuts around openings; the second column below already includes it.
| Area | 4 × 8 sheets | With 10% waste |
|---|---|---|
| 400 sq ft | 13 | 14 |
| 800 sq ft | 25 | 28 |
| 1200 sq ft | 38 | 42 |
| 2000 sq ft | 63 | 69 |
Divide the total area you're covering by the coverage of one panel. A standard 4x8 sheet covers 32 square feet, so divide your square footage by 32 and add 10% for waste and cuts.
Divide the total roof area (including the pitch factor) by 32 square feet per sheet, then add about 10% for waste. A 1,600 sq ft roof needs roughly 50 sheets plus waste.
Roof sheathing is typically 7/16-inch OSB or 15/32-inch plywood for rafters 24 inches on center. Wall sheathing is usually 7/16-inch OSB. Subfloors use thicker 3/4-inch tongue-and-groove panels.
Roof and wall sheathing is nailed roughly every 6 inches along panel edges and 12 inches in the field, which works out to about 60 nails per 4x8 sheet, or roughly 1 pound of nails for every 3 to 4 sheets.
Yes. Leave about a 1/8-inch gap between panels (the thickness of an 8d nail) so they can expand with humidity without buckling. Many OSB panels have spacer lugs built into the edges.
Both are code-approved structural panels. OSB is cheaper and more uniform; plywood is lighter, dries faster if it gets wet, and holds fasteners slightly better. Most new construction uses OSB.
8d common nails, 0.131 in. by 2-1/2 in., are the IRC minimum for wood structural panel roof sheathing. Space them 6 in. on center where panel edges bear on framing and 12 in. on center at intermediate supports. High-wind jurisdictions often require a tighter pattern and ring-shank nails, so check local amendments.
6 in. on center at supported panel edges and 12 in. on center in the field, known as the 6/12 pattern. Keep nails at least 3/8 in. in from panel edges and leave a 1/8 in. gap between panel ends and edges.
Every constant this calculator uses and where it comes from, so you can check it rather than take our word for it.
Local codes amend the model IRC and adopt different cycles — your building department governs. Manufacturers revise yields; where your product's data sheet disagrees with a default here, use the product's number. See our full methodology.