Plywood and OSB sheathing calculator

Pick a roof, wall or floor and enter its size, the sheet size, the framing spacing and your waste. Get the sheet count, the lightest span rating that works from the IRC table, the panel clips a roof needs, and the nails.

32 sq ftIn a 4 × 8 sheet

16/0 to 60/32Span ratings covered

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Sheets

1,901 sq ft of roof, 4 × 8 ft sheets

24/0, 3/8 in.Panel

2,178Nails

264Clips

The code adopted where you work, the panel maker and the inspector govern spans and nailing.

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How we got this

Area1,700 sq ft × 1.118 (pitch factor for 6/12) = 1,901 sq ftThe pitch factor turns the flat footprint into the sloped area: √(1 + (rise ÷ 12)²).
Sheets1,901 sq ft × 1.10 ÷ 32 sq ft a sheet = 66 sheets
Span rating24/0 (3/8 in.) with edge support; or 24/16 (7/16 in.) without clipsFrom IRC Table R503.2.1.1(1). The first number of a span rating is the longest roof span, the second the longest floor span. Panels run with the long side across three or more supports.
Panel clips96 in. ÷ 24 in. = 4 a sheet × 66 = 264 clipsEdge support is blocking, tongue and groove edges or a panel clip midway between each pair of supports (two between supports at 48 in.), per footnote d of the table.
Nails33 a sheet × 66 = 2,178 nails8d at 6 in. on panel edges and 12 in. on intermediate supports (10 in. on floors), as the Laguna Hills framing sheet shows for 1/2 in. panels. Your code's fastener schedule, the shear wall or diaphragm plan and high-wind rules can call for closer spacing.

Item	Quantity	Basis
4 × 8 ft sheets	66	1,901 sq ft + 10%
Panel clips	264	4 a sheet
8d nails	2,178	33 a sheet

Sources: IRC Table R503.2.1.1(1), allowable spans for wood structural panels (City of Republic, MO handout); City of Laguna Hills, Conventional wood-frame construction sheet (2022 CRC summary, sheathing nailing). Checked 2026-10-08.

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Key takeaways

Sheets = area × (1 + waste) ÷ 32 for 4 × 8. A roof's area is its footprint times the pitch factor: 1.118 at 6/12.
The span rating stamped on the panel is two numbers: the first is the longest roof span, the second the longest floor span. Rafters at 24 in. need a 24 rating; joists at 16 in. need a 16.
Roof panels without blocked or tongue and groove edges can need panel clips, one between each pair of rafters. Nail at 6 in. on the edges and 12 in. in the field (10 in. on floors) unless your plan says closer.

How many sheets of plywood do I need

Divide the area by the area of one sheet, after adding waste:

Sheets = area × (1 + waste) ÷ sheet area

A 4 × 8 sheet is 32 sq ft, a 4 × 9 is 36 and a 4 × 10 is 40. The longer sheets are for walls taller than 8 ft, so one sheet covers from the plate to the band without a seam.

Walls: length × height, less the openings if their cut-outs will be used elsewhere. If you sheathe over the openings and cut them out afterward, leave them in.
Roofs: the footprint from above, with the overhangs, times the pitch factor. The pitch factor is √(1 + (rise ÷ 12)²), the length of the slope for every foot of run.
Floors: length × width of the floor.

Roof pitch	Pitch factor	1,500 sq ft footprint	4 × 8 sheets at 10% waste
4/12	1.054	1,581 sq ft	55
6/12	1.118	1,677 sq ft	58
8/12	1.202	1,803 sq ft	62
10/12	1.302	1,953 sq ft	68
12/12	1.414	2,121 sq ft	73

Waste is yours to set. Simple gable roofs and long plain walls waste little; hips, valleys, dormers, gable ends and lots of windows waste more. Use what your own jobs run.

Span ratings: what thickness for rafters and joists

Structural plywood and OSB carry a span rating on the grade stamp, such as 24/16 or 32/16. The first number is the longest roof span in inches, with the panel's long side across three or more supports and the edges supported. The second is the longest floor span. Panels marked with a single number, such as 20 o.c., are single floor panels that serve as subfloor and underlayment in one.

These are from IRC Table R503.2.1.1(1), which covers roof sheathing and subfloor:

Span rating	Thickness, in.	Roof, edges supported	Roof, no edge support	Subfloor
16/0	3/8	16 in.	16 in.	n/a
20/0	3/8	20 in.	20 in.	n/a
24/0	3/8	24 in.	20 in.	n/a
24/16	7/16	24 in.	24 in.	16 in.
32/16	15/32, 1/2	32 in.	28 in.	16 in.
40/20	19/32, 5/8	40 in.	32 in.	20 in.
48/24	23/32, 3/4	48 in.	36 in.	24 in.
60/32	7/8	60 in.	48 in.	32 in.

Single floor panels in the same table: 16 o.c. and 20 o.c. at 19/32 or 5/8 in., 24 o.c. at 23/32 or 3/4 in., 32 o.c. at 7/8 in., and 48 o.c. at 1 1/8 in. Their edges need tongue and groove or blocking unless an underlayment or a 3/4 in. wood floor laid across the joists goes on top.

The calculator picks the lightest rating that covers your spacing. That is the minimum the table allows; you can always choose a thicker panel for a stiffer floor or a flatter roof.

Plywood or OSB, and reading the grade stamp

The IRC treats plywood and OSB the same way: both are wood structural panels, and both use the same span table. What matters is the grade stamp, not the type of panel. The code requires structural panels to meet DOC PS 1 or DOC PS 2 (or the Canadian CSA standards when made in Canada), and to carry a grade mark from an approved agency showing the grade, the bond classification and the Performance Category.

The Performance Category is the thickness the code uses. A panel stamped 15/32 Performance Category is treated as 15/32 in. for every rule in the code, even if it measures a hair different. Read the stamp on the panels you buy and check three things:

Span rating matches or beats the one the calculator gives for your spacing.
Bond classification suits the exposure on your job.
Performance Category matches the thickness on your plans.

Panels are stronger with their long side, the strength axis, running across the supports. The spans in the table assume exactly that, with each panel continuous over two or more spans. Turn a panel the other way and it will not carry the rated span.

Do I need H-clips on roof sheathing

Look at the two roof columns of the table. The "no edge support" span is shorter than the "edges supported" span for most ratings. Where your rafter or truss spacing is longer than the no edge support figure, the long edges between rafters need support: blocking, tongue and groove edges, or panel edge clips.

Footnote d of the table says how many clips: one midway between each pair of supports, or two equally spaced when the span is 48 in. A 4 × 8 sheet laid across trusses at 24 in. has four spaces along its long edge, so it takes four clips. The calculator counts them for you.

At 24 in., a 24/0 panel (3/8 in.) needs clips because its no edge support span is 20 in.; a 24/16 panel (7/16 in.) does not, because it spans 24 in. either way. Price both: sometimes the thicker panel costs less than the thinner one plus clips and the time to set them.

How many nails per sheet of plywood

A common schedule is 8d nails at 6 in. along the panel edges and 12 in. along the supports in between on roofs and walls, and 10 in. in between on floors, as on the conventional framing sheet the City of Laguna Hills publishes for 1/2 in. panels. On a 4 ft wide sheet the 10 in. floor spacing still lands 5 nails on each inner support, so the counts below hold for both. Here is how that works out per sheet:

Sheet and use	Framing	Nails per sheet	How
4 × 8 roof or floor	16 in.	43	2 edge supports × 9 + 5 inner supports × 5
4 × 8 roof or floor	24 in.	33	2 × 9 + 3 × 5
4 × 8 wall	16 in.	66	2 edge studs × 17 + plates 2 × 7 + 2 inner studs × 9
4 × 8 wall	24 in.	57	2 × 17 + 2 × 7 + 1 × 9
4 × 9 wall	16 in.	72	2 × 19 + 2 × 7 + 2 × 10

Shear walls, roof diaphragms and high-wind areas often call for closer nailing on the edges and boundaries, and some plans specify other nails. Use the schedule on your plans or in the fastener table of your code when it differs; the count here is for ordering, not for design.

Worked examples

A roof. A 1,700 sq ft footprint at 6/12 with trusses at 24 in. Area: 1,700 × 1.118 = 1,901 sq ft. Sheets: 1,901 × 1.10 ÷ 32 = 65.3, so 66. Rating: 24/0 with clips, 4 a sheet, 264 clips; or 24/16 (7/16 in.) with no clips. Nails: 33 a sheet × 66 = 2,178.

A subfloor. 1,200 sq ft over joists at 16 in., 5% waste. Sheets: 1,200 × 1.05 ÷ 32 = 39.4, so 40. Rating: 24/16 sheathing under an underlayment, or a 16 o.c. single floor panel (19/32 or 5/8 in.) with tongue and groove edges. Nails: 43 a sheet, 1,720.

Walls 9 ft high. 140 ft of wall, 4 × 9 sheets so each sheet runs plate to plate, 10% waste. Area: 1,260 sq ft. Sheets: 1,260 × 1.10 ÷ 36 = 38.5, so 39. Nails: 72 a sheet, 2,808. The panel itself comes from your wall bracing plan, not from the roof and floor table.

Press "Save as an estimate in Koira" to carry the sheets, clips and the area to install as lines. Price them and send the estimate. For the studs and headers behind the sheathing, use the framing calculator; for the roof itself, the roof replacement cost calculator.

The code and the inspector governSpans and nailing here come from the IRC table and a city's published framing sheet. Your adopted code, the panel maker's instructions, the plans and the local inspector decide what is allowed, especially for shear walls, diaphragms and high-wind areas.

Last checked October 8, 2026. More for your trade: how roofers run on Koira.

FAQ

How many sheets of plywood do I need for a roof?

Footprint × pitch factor = roof area; add waste and divide by 32 for 4 × 8 sheets. A 1,700 sq ft footprint at 6/12 is 1,901 sq ft of roof, which is 66 sheets with 10% waste.

What does 24/16 mean on plywood?

It is the span rating. The panel can span 24 in. between rafters on a roof and 16 in. between joists on a floor, with its long side across three or more supports.

What thickness plywood for a roof with rafters at 24 inches?

The IRC table allows a 24/0 panel (3/8 in.) with edge support such as clips, or a 24/16 panel (7/16 in.) without.

What thickness subfloor for joists at 16 inches?

24/16 or 32/16 sheathing (7/16 or 15/32 in.) under an underlayment, or a 16 o.c. single floor panel (19/32 or 5/8 in.). At 24 in., 48/24 sheathing (23/32 or 3/4 in.) or a 24 o.c. single floor panel.

How many nails per sheet of plywood?

With 8d at 6 in. on the edges and 12 in. in the field (10 in. on floors), about 43 on a 4 × 8 roof or floor sheet over 16 in. framing, 33 over 24 in., and 66 on a 4 × 8 wall sheet on studs at 16 in.

Do I need H-clips?

Where the rafter or truss spacing is more than the panel's no edge support span and the edges are not blocked or tongue and groove. At 24 in., a 24/0 panel needs them and a 24/16 panel does not.

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