Roof, wall and floor sheathing all come in 4x8 sheets, but the panel you need depends on the job and on how far apart the rafters, studs or joists are. The code tables behind it are the International Residential Code's sheathing tables.
How to use this calculator
- Pick roof, wall, subfloor or single-layer floor.
- Enter the size. For a roof, enter the footprint with the overhangs and the pitch; the calculator adds the slope.
- Choose the framing spacing and the panel you plan to buy.
- Under More options, change the extra for waste if the roof or plan is cut up.
Worked examples
A gable roof
What you are covering: Roof sheathing · Size: 40 × 28 ft · Roof pitch: 6 in 12 · Rafters, studs or joists on center: 24 in · Panel: 7/16 in OSB
- Sheets
- 44 4 x 8 ft sheets
- Nails or screws, about
- 1,460
- Panel edge clips (H-clips), if used
- 176
- Area to cover
- 1,252 sq ft
- Weight of the sheets
- 2,024 lb
- Each sheet weighs
- 46 lb
- Thinnest panel the IRC allows here
- 7/16 in
Wall sheathing for a garage
What you are covering: Wall sheathing · Wall length, all walls: 88 ft · Wall height: 8 ft · Doors and windows to subtract: 120 sq ft · Rafters, studs or joists on center: 16 in · Panel: 7/16 in OSB
- Sheets
- 21 4 x 8 ft sheets
- Nails or screws, about
- 910
- Area to cover
- 584 sq ft
- Weight of the sheets
- 966 lb
- Each sheet weighs
- 46 lb
- Thinnest panel the IRC allows here
- 3/8 in
A subfloor
What you are covering: Subfloor under underlayment · Size: 32 × 24 ft · Rafters, studs or joists on center: 16 in · Panel: 5/8 in plywood
- Sheets
- 27 4 x 8 ft sheets
- Nails or screws, about
- 1,170
- Area to cover
- 768 sq ft
- Weight of the sheets
- 1,555 lb
- Each sheet weighs
- 58 lb
- Thinnest panel the IRC allows here
- 7/16 in
A single-layer floor on wide joists
What you are covering: Single-layer floor · Size: 24 × 20 ft · Rafters, studs or joists on center: 24 in · Panel: 3/4 in OSB
- Sheets
- 17 4 x 8 ft sheets
- Nails or screws, about
- 570
- Area to cover
- 480 sq ft
- Weight of the sheets
- 1,360 lb
- Each sheet weighs
- 80 lb
- Thinnest panel the IRC allows here
- 23/32 in
How many sheets
Each 4x8 sheet covers 32 square feet. Divide the area by that and add an allowance for cutting waste: a Forest Service and APA study of house building used 10 percent for panels. A roof with hips, valleys and dormers wastes more.
For a roof, the slope makes the surface bigger than the footprint, which is why the calculator asks for the pitch.
How thick the panels must be
- Roof on rafters 16 in apart: at least 3/8 in.
- Roof on rafters 24 in apart: 7/16 in with no edge support, or 3/8 in only with edge clips or blocking between the rafters.
- Wall sheathing on studs 16 in apart: at least 3/8 in.
- Subfloor under underlayment: 7/16 in on joists 16 in apart, 19/32 in at 19.2 in and 23/32 in at 24 in.
- A single-layer floor, with no underlayment: 19/32 in on joists 16 in apart and 23/32 in at 24 in.
- These are the code's minimums by span rating; the rating stamped on the panel decides, and your plans may call for thicker panels.
What the sheets weigh
Half-inch plywood weighs about 1.5 lb per square foot and half-inch OSB about 1.7 lb per square foot, while a 4x8 sheet of 7/16 in OSB weighs about 46 lb. Three-quarter-inch panels run 2.3 lb per square foot for plywood and 2.5 lb per square foot for OSB. Check the truck's payload before a big load.
Nails and edge clips
Sheathing is nailed every 6 inches along supported edges and every 12 inches on the framing in between; the calculator counts that pattern. On a roof with rafters wide apart, thin panels need edge support between the rafters: the IRC calls for 1 clip edge clip midway between each pair of supports.
Common questions
How many sheets of plywood do I need?
Divide the area by 32 square feet per sheet and add about 10 percent for cuts. For a roof, use the sloped area, not the footprint; the calculator handles both.
What thickness of plywood for a roof?
On rafters 24 in apart, 7/16 in without edge clips is the minimum; on rafters 16 in apart, 3/8 in will do. The span rating stamped on the panel is what counts.
How much does a sheet of plywood weigh?
About 1.5 lb per square foot for half-inch plywood, so a 4x8 sheet weighs a few dozen pounds; the calculator gives the weight of each sheet and of the whole load.
Is OSB or plywood better for a roof?
Both are allowed when they carry the right span rating. OSB costs less and weighs a little more for the same thickness; plywood handles getting wet during construction a bit better.
Do I need H-clips on roof sheathing?
Only where the panels need edge support between rafters: on rafters 24 in apart with panels of 3/8 in, for example. Panels of 7/16 in or thicker on rafters 24 in apart do not need them.