How many sheets of plywood or OSB do I need?

Work out the area you are covering, add 10% for waste and divide by the area of one panel: 32 sq ft for 4 × 8 ft, 36 for 4 × 9 and 40 for 4 × 10. Round up. A roof deck uses the true roof area, the footprint (with overhang) times the pitch factor. The example house is 1,503 sq ft of roof, which is 52 panels of 4 × 8 ft with 10% waste.

How much waste should I allow for sheathing?

About 10% for a plain gable roof, a wall or a subfloor, and about 15% for a hip roof, where the diagonal hips and valleys cut panels into pieces that rarely get reused. Those are typical figures, not rules, and both are presets here with room to enter your own. Many openings, short walls or odd shapes need more.

How do I find the roof area from the footprint?

Multiply the footprint (length × width, plus the overhang on every side) by the pitch factor, √(1 + (rise ÷ 12)²). For 1,344 sq ft of footprint at 6/12 the pitch factor is 1.118, so the roof deck is 1,503 sq ft. The slope calculator turns an angle, a percent grade or a rise and run into x/12. The table on this page lists panel counts for common footprints at 4/12, 6/12 and 8/12.

How many sheets for the walls of a house?

Multiply the total wall length by the wall height and subtract large openings. A 140 ft run of 8 ft walls is 1,120 sq ft, which is 39 panels of 4 × 8 ft with 10% waste before taking off any windows or doors. The wall example further down shows 9 ft walls with 4 × 9 ft panels and five openings taken off.

What are H-clips and do I need them?

H-clips (panel edge clips) snap onto the long edges where two roof panels meet between rafters, holding the edges level so the deck does not ripple. Roof panels thin enough to span 24 in between supports are commonly used with one clip midway between the supports, so a 4 × 8 ft panel with rafters 24 in on center takes about 4. Some panel makers and codes call for them and some accept tongue-and-groove edges or blocking instead; check your panel's instructions and local code. The count here is an estimate, and it only appears for a roof deck with supports 24 in on center.

How many nails per sheet of sheathing?

A commonly published schedule is nails 6 in apart along the panel edges and 12 in apart in the field, on each support. With the panel's long side across supports 24 in on center that is about 28 nails for a 4 × 8 ft panel: 1,315 for the example roof. Treat it as an estimate. The nail type and size, the spacing at gable ends and in high-wind or seismic zones, and the schedule for walls and floors come from the panel maker and local code; follow those, and buy extra, since misfires happen.

What thickness or span rating of plywood or OSB should I use?

That is a structural choice and this calculator does not make it. Panels carry a span rating on their stamp, a pair of numbers such as 24/16: roughly, the widest rafter spacing it is rated to span as roof sheathing and the widest joist spacing as subfloor. Your framing spacing, roof and floor loads, the finish on top and local code decide what you need, and a designer, supplier or building department can confirm it.

Is 4 × 8, 4 × 9 or 4 × 10 better?

Taller panels mean fewer pieces to hang and fewer seams, and 4 × 9 and 4 × 10 suit walls taller than 8 ft. They are heavier and harder to carry up a ladder or onto a roof, and cost more per panel (though less per sq ft in some stores). Count with the size you can actually buy: the table on this page shows panels per 1,000 sq ft for each. A 1220 × 2440 mm metric panel is close to 4 × 8 ft.

Does this count underlayment, flashing or shingles?

No. It counts sheathing panels, and the H-clips and nails for them. For the roofing on top, use the roofing shingles calculator, which counts bundles, underlayment, starter and ridge cap.

Plywood & OSB Sheathing Calculator: How Many Panels Do I Need?

Sheets of plywood or OSB = area × 1.10 ÷ the area of one panel (32 sq ft for 4 × 8 ft), rounded up. A 40 × 30 ft house with a 12 in overhang and a 6/12 gable roof has 1,344 sq ft of footprint, which is 1,503 sq ft of actual roof (footprint × pitch factor 1.118): 52 panels of 4 × 8 ft with 10% waste. With rafters or trusses 24 in on center, an estimate for the H-clips is 188 and for the nails is 1,315. This counts material only: the panel thickness and span rating are a structural choice for your framing, loads and local code.

Figures based on the sources listed belowUpdated 2026-10-04How we calculate

Length (or total wall length)

Width (or wall height)

Waste

Typical: gable roof, walls, floors (10%)Typical: hip roof (15%)Custom

What are you sheathing?Roof deck: enter the building footprint, and the pitch below. Wall: enter the total wall length and the wall height. Subfloor: enter the floor length and width.

Panel sizePlywood and OSB are sold 4 ft wide in 8, 9 and 10 ft lengths in the US; 1220 × 2440 mm is the metric panel. Longer panels mean fewer seams but are harder to handle.

Roof pitch (rise per 12 in of run, x/12)

A 6 means the roof rises 6 in for every 12 in across. Use the slope calculator if you only have an angle or a percent.

Overhang (in)

How far the roof deck sticks out past the walls, added on every side. Use 0 if the length and width you entered already include it.

Rafter, stud or joist spacingSets the nail count, and whether a roof deck is counted for H-clips: they are a common way to support the unsupported edges when rafters or trusses are 24 in on center.

Price per panel (optional)

Buy 52 panels

1,502.64 sq ft + 10% waste = 1,652.90 sq ft

H-clips (estimate, one per bay on each panel’s long edge): 188 clips
Nails, 6 in on edges and 12 in in the field (estimate): 1,315 nails

Low

$780.00

Expected

$1,144.00

High

$1,664.00

Includes 150.26 sq ft waste

How this number is calculated

1,502.64 sq ft + 10% waste = 1,652.90 sq ft ÷ 32 sq ft per panel = 52 panels

Shopping list

H-clips for 7/16 in or 15/32 in roof sheathing
Ring-shank or coil sheathing nails (8d)
Framing nailer
Chalk line
Circular saw
Panel carrier handles
Roof harness and rope grab kit
Subfloor construction adhesive

Show diagram

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Panels of 4 × 8 ft sheathing for a roof by footprint and pitch

Gable roof, no overhang, 10% waste, worked by this calculator. Add the overhang to each side first if you measured the walls, use 15% for a hip roof, and subtract skylights and chimneys in the calculator.
Footprint	4/12 pitch	6/12 pitch	8/12 pitch
30 × 20 ft (600 sq ft)	22	24	25
40 × 25 ft (1,000 sq ft)	37	39	42
50 × 30 ft (1,500 sq ft)	55	58	62
50 × 40 ft (2,000 sq ft)	73	77	83
60 × 40 ft (2,400 sq ft)	87	93	100

Panel sizes and the per-panel estimates used here

Worked by this calculator. Panels per 1,000 sq ft include 10% waste. H-clips and nails are estimates per panel at supports 24 in on center, long side across the supports.
Panel size	Area (sq ft)	Panels per 1,000 sq ft	H-clips per panel (roof)	Nails per panel
4 × 8 ft	32	35	4	28
4 × 9 ft	36	31	5	32
4 × 10 ft	40	28	5	32
1220 × 2440 mm (metric)	32	35	4	28

Methodology & assumptions

Pick what you are sheathing. For a roof deck, enter the building's footprint (length × width from above); the calculator adds the overhang on every side, then multiplies by the pitch factor, √(1 + (rise ÷ 12)²), the same way as the roofing shingles calculator, which holds for a gable or hip roof when every plane has the same pitch. For a wall, enter the total wall length and the wall height; for a subfloor, the floor length and width. Subtract openings (windows, doors, skylights, stairwells). The area is multiplied by 1 plus the waste allowance (10% by default; 15% is typical for a hip roof, whose diagonal cuts leave more offcuts) and divided by the area of one panel: 32 sq ft for 4 × 8 ft, 36 for 4 × 9, 40 for 4 × 10 and 32.04 for a 1220 × 2440 mm panel, rounded up to whole panels. The H-clip and nail counts are estimates on the net area (no waste), assuming the long side of each panel runs across the supports and its short ends land on one. H-clips are counted for a roof deck with rafters or trusses 24 in on center only: one clip midway between supports along each panel's unsupported long edge, so as many as there are bays along the long side (4 for a 4 × 8 ft panel at 24 in). Nails use a commonly published schedule of 6 in apart along the supported panel edges and 12 in apart on the supports in the field, which is 28 per 4 × 8 ft panel at 24 in on center. The nailing schedule, nail size and clip use for your panels come from the panel maker, the framing and local code, so follow those. Thickness and span rating are not chosen here: a panel's span rating is a pair of numbers, such as 24/16, for the widest spacing of rafters (roof) and joists (floor) it is rated to span, and your framing spacing, loads and code set what you need. Waste for a roof also depends on how the panels stagger; this is a material count, not a layout or a structural design. The metric toggle shows lengths in m and areas in m².

APA, The Engineered Wood Association, Engineered Wood Construction Guide (Form E30): span ratings (such as 24/16), panel edge clips for roof sheathing, and recommended nailing, commonly 6 in at panel edges and 12 in at intermediate supports
APA, Performance Rated Panels (Form E30 and the panel trademark): the span rating on the panel stamp is the maximum support spacing for roof and for floor use
Your local building code and the panel and nail manufacturer’s instructions: required thickness, span rating, nailing schedule and edge support for your framing and loads
Pitch factor √(1 + (rise ÷ 12)²): the slope length of a roof for each unit of horizontal run (the Pythagorean theorem)
Typical US retail prices for 7/16 in to 3/4 in OSB and plywood sheathing panels, 2026 (estimate)

How to calculate plywood or OSB sheathing

Pick roof, wall or subfloor. Choose what you are covering. A roof deck takes the building footprint and the pitch; a wall takes the total wall length and height; a subfloor takes the floor length and width.
Measure and enter the area. For a roof, enter the footprint, the overhang and the x/12 pitch: the calculator multiplies the footprint by the pitch factor to get the true roof area. Add windows, doors, skylights or stairwells as openings.
Choose the panel size. Pick 4 × 8, 4 × 9, 4 × 10 or 1220 × 2440 mm panels, the size you can actually buy and handle.
Add waste. Use 10% for a gable roof, wall or floor and 15% for a hip roof, or your own figure for a complicated job.
Divide by the panel area and round up. Divide the area with waste by the area of one panel and round up to whole panels. For a roof with rafters 24 in on center the calculator also estimates H-clips, and it estimates nails for any mode; confirm the nailing schedule with the panel maker and local code.

Worked examples

Project	Result
40 × 30 ft house, 6/12 gable roof, 12 in overhang, 4 × 8 ft panels, rafters 24 in on center	About 1,503 sq ft of roof + 10% waste → 52 panels, about 188 H-clips and 1,315 nails
50 × 30 ft house, 8/12 hip roof, 12 in overhang, 4 × 10 ft panels, 15% waste	About 2,000 sq ft of roof + 15% waste → 58 panels, about 250 H-clips
140 ft of 9 ft walls (a 40 × 30 ft house) with a door and four windows taken off, 4 × 9 ft panels, 10% waste	About 1,192 sq ft of wall + 10% waste → 37 panels
24 × 16 ft addition subfloor, a 3 × 10 ft stairwell taken off, 4 × 8 ft panels, joists 16 in on center, 10% waste	About 354 sq ft of floor + 10% waste → 13 panels, about 399 nails

Frequently asked questions

How many sheets of plywood or OSB do I need?: Work out the area you are covering, add 10% for waste and divide by the area of one panel: 32 sq ft for 4 × 8 ft, 36 for 4 × 9 and 40 for 4 × 10. Round up. A roof deck uses the true roof area, the footprint (with overhang) times the pitch factor. The example house is 1,503 sq ft of roof, which is 52 panels of 4 × 8 ft with 10% waste.
How much waste should I allow for sheathing?: About 10% for a plain gable roof, a wall or a subfloor, and about 15% for a hip roof, where the diagonal hips and valleys cut panels into pieces that rarely get reused. Those are typical figures, not rules, and both are presets here with room to enter your own. Many openings, short walls or odd shapes need more.
How do I find the roof area from the footprint?: Multiply the footprint (length × width, plus the overhang on every side) by the pitch factor, √(1 + (rise ÷ 12)²). For 1,344 sq ft of footprint at 6/12 the pitch factor is 1.118, so the roof deck is 1,503 sq ft. The slope calculator turns an angle, a percent grade or a rise and run into x/12. The table on this page lists panel counts for common footprints at 4/12, 6/12 and 8/12.
How many sheets for the walls of a house?: Multiply the total wall length by the wall height and subtract large openings. A 140 ft run of 8 ft walls is 1,120 sq ft, which is 39 panels of 4 × 8 ft with 10% waste before taking off any windows or doors. The wall example further down shows 9 ft walls with 4 × 9 ft panels and five openings taken off.
What are H-clips and do I need them?: H-clips (panel edge clips) snap onto the long edges where two roof panels meet between rafters, holding the edges level so the deck does not ripple. Roof panels thin enough to span 24 in between supports are commonly used with one clip midway between the supports, so a 4 × 8 ft panel with rafters 24 in on center takes about 4. Some panel makers and codes call for them and some accept tongue-and-groove edges or blocking instead; check your panel's instructions and local code. The count here is an estimate, and it only appears for a roof deck with supports 24 in on center.
How many nails per sheet of sheathing?: A commonly published schedule is nails 6 in apart along the panel edges and 12 in apart in the field, on each support. With the panel's long side across supports 24 in on center that is about 28 nails for a 4 × 8 ft panel: 1,315 for the example roof. Treat it as an estimate. The nail type and size, the spacing at gable ends and in high-wind or seismic zones, and the schedule for walls and floors come from the panel maker and local code; follow those, and buy extra, since misfires happen.
What thickness or span rating of plywood or OSB should I use?: That is a structural choice and this calculator does not make it. Panels carry a span rating on their stamp, a pair of numbers such as 24/16: roughly, the widest rafter spacing it is rated to span as roof sheathing and the widest joist spacing as subfloor. Your framing spacing, roof and floor loads, the finish on top and local code decide what you need, and a designer, supplier or building department can confirm it.
Is 4 × 8, 4 × 9 or 4 × 10 better?: Taller panels mean fewer pieces to hang and fewer seams, and 4 × 9 and 4 × 10 suit walls taller than 8 ft. They are heavier and harder to carry up a ladder or onto a roof, and cost more per panel (though less per sq ft in some stores). Count with the size you can actually buy: the table on this page shows panels per 1,000 sq ft for each. A 1220 × 2440 mm metric panel is close to 4 × 8 ft.
Does this count underlayment, flashing or shingles?: No. It counts sheathing panels, and the H-clips and nails for them. For the roofing on top, use the roofing shingles calculator, which counts bundles, underlayment, starter and ridge cap.

Handy tools

Slope Calculator: Turn a rise and run, an angle or a percent grade into the x/12 pitch the roof field takes.