Plywood Calculator
Calculate how many sheets of plywood or OSB you need for a subfloor, wall sheathing or roof deck from the area, sheet size and waste, plus fasteners and cost.
By CalcBuilt Editorial TeamUpdated September 10, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Sheets to buy
- 11 sheets
- 4 x 8 ft sheets covering 352 sq ft
- Area to cover
- 352 sq ft
- 320 sq ft plus 10% waste
- Nails or screws
- 660
- About 60 per sheet at 6 in on edges and 12 in in the field; 8d common for sheathing (IRC Table R602.3(1)), ring-shank nails or 2 in screws plus adhesive for subfloor
Plywood formula
Area (sq ft) = Length x Width + extra areas
Area with waste = Area x (1 + waste %)
Sheets = Area with waste / sheet area (4x8 = 32, 4x10 = 40, 4x12 = 48), rounded up
Fasteners = Sheets x about 60 per 4 x 8 sheetWorked example
A gable roof with two planes each 40 x 12 ft: 2 x 480 = 960 sq ft. Add 10% waste for 1,056 sq ft. Divided by 32 sq ft per sheet that is 33 sheets of 4 x 8 OSB, and about 1,980 nails.
Quick reference
| Area | With 10% waste | 4 x 8 sheets |
|---|---|---|
| 100 sq ft | 110 sq ft | 4 |
| 200 sq ft | 220 sq ft | 7 |
| 320 sq ft | 352 sq ft | 11 |
| 500 sq ft | 550 sq ft | 18 |
| 800 sq ft | 880 sq ft | 28 |
| 1,000 sq ft | 1,100 sq ft | 35 |
How to calculate plywood sheets
Measure each surface and add them up: every wall, each roof plane, or the whole floor. Divide by the sheet area and round up. Waste comes from layout, not the saw: sheets run with the long edge across the framing and joints staggered, so the half-sheet drop from one course starts the next. Hips, valleys and dormers leave triangles that fit nowhere, so use 15 percent there and 10 on a rectangle.
A 4x8 sheet is stock everywhere and is what one person carries up a ladder. On a 9 ft wall it leaves a horizontal seam that needs 2x blocking behind it in a braced wall panel (IRC R602.10.10). 4x9 or 4x10 sheets from a lumber yard run full height and skip the blocking. Leave a 1/8 in gap at every edge and end, OSB or plywood.
Which thickness to buy
Read the APA stamp: the span rating is roof/floor in inches, so 24/16 on 7/16 OSB means rafters to 24 in and joists to 16 in. Common ratings are 32/16 on 15/32 and 48/24 on 23/32 tongue-and-groove subfloor. Subfloor: 23/32 T&G over joists at 16 or 24 in, glued with ASTM D3498 adhesive and fastened with ring-shank nails or 2 in screws. The glue is what stops squeaks. Wall sheathing: 7/16 OSB or 15/32 CDX with 8d common nails at 6 in on edges and 12 in in the field (IRC Table R602.3(1)). Roof decking: 7/16 OSB on rafters at 24 in needs an H-clip in every bay; 15/32 (32/16) does not (IRC Table R503.2.1.1(1)). OSB edges swell when wet, so dry in a subfloor within days or buy a premium subfloor with a sealed edge.
What this calculator leaves out
H-clips (about 4 per sheet on a 24 in roof) and subfloor adhesive (one 28 oz tube per about 3 sheets). Also house wrap and seam tape, roofing underlayment, blocking behind horizontal wall seams, and drip edge. It does not deduct openings: estimators leave doors and windows in the count because the drops rarely fit anywhere else.
Mistakes that cost money
- 4x8 sheathing on a 9 ft wall: the horizontal seam needs 2x blocking behind it in a braced wall (IRC R602.10.10); 4x9 sheets skip it.
- 7/16 OSB on rafters at 24 in with no H-clips: the unsupported edges sag between rafters and telegraph through the shingles.
- OSB subfloor left open to a week of rain: the edges swell 1/8 in and show through vinyl; sand the seams flat before flooring.
- Subfloor nailed with smooth-shank nails and no adhesive squeaks within a year; use ASTM D3498 subfloor adhesive with ring-shank nails or 2 in screws.
- Panels butted tight with no 1/8 in gap: a summer of humidity buckles the roof deck into ridges you can see from the street.
- Roof OSB laid smooth side up: the stamp reads This side down for a reason; the screened face up gives roofers footing.
Key facts
- A 4 x 8 ft sheet covers 32 sq ft; 4 x 10 covers 40 and 4 x 12 covers 48.
- Subfloors use 23/32 in (3/4 nominal) tongue-and-groove plywood or OSB stamped 48/24, glued and screwed, over joists at 16 or 24 in on center.
- Wall sheathing is commonly 7/16 in OSB or 15/32 in plywood. On a roof at 24 in on center, 7/16 OSB (24/16) needs an H-clip in every rafter bay; 15/32 (32/16) does not.
- Nail sheathing with 8d common nails at 6 in on center along panel edges and 12 in in the field, about 60 nails per 4 x 8 sheet.
- Leave a 1/8 in gap between sheets, OSB or plywood, so they can expand without buckling.
Frequently asked questions
How many sheets of plywood for a 20x16 floor?
320 sq ft plus 10% waste is 352 sq ft, which is 11 sheets of 4 x 8 plywood.
Do I need to glue the subfloor?
Yes. Run a 1/4 in bead of ASTM D3498 subfloor adhesive on every joist and in the groove, and set the sheet within the open time on the tube. Fasten with ring-shank nails or 2 in screws at 6 in on edges and 12 in in the field. Glue plus screws is what stops squeaks; nails alone loosen as the joists dry. One 28 oz tube does about 3 sheets.
Should I use plywood or OSB for sheathing?
Both are rated for structural sheathing. OSB is cheaper and comes in larger sheets; plywood holds fasteners a little better and tolerates moisture better at the edges. Follow the span rating stamp either way.
How many nails per sheet of plywood?
About 60 for a 4 x 8 sheet: 8d nails every 6 in along the edges and every 12 in on intermediate supports.
Sources and references
- How to Read an APA Trademark Stamp (APA The Engineered Wood Association)
- Proper Installation of APA Rated Sheathing for Roof Applications (APA The Engineered Wood Association)
- Underlayment and subfloor panel guidance (APA The Engineered Wood Association)
- Chapter 5 Floors, 2021 IRC (ICC)
Next steps for this project
The usual order for a framing, decks & fences project. See all framing, decks & fences calculators.
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.