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 9, 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
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 you are covering and add them up: every wall, each roof plane, or the whole floor. Add 10 percent for straight cuts and 15 percent where there are hips, valleys, dormers or many windows. Divide by the sheet area and round up. Sheets are laid with the long edge across the framing and joints staggered, so some offcuts cannot be reused.
A 4 x 8 sheet is the practical choice for almost everything. Longer sheets reduce joints on tall walls but are hard to handle on a roof.
Which thickness to buy
Subfloor: 3/4 in tongue-and-groove plywood or OSB rated for the joist spacing, glued and screwed. Wall sheathing: 7/16 in OSB or 1/2 in CDX plywood is standard. Roof decking: 1/2 in on rafters at 16 in on center, 5/8 in at 24 in, with H-clips between rafters. Look for the APA span rating stamp on the sheet, which tells you the maximum support spacing for roofs and floors.
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 3/4 in tongue-and-groove plywood or OSB over joists at 16 in on center.
- Wall sheathing is commonly 7/16 in OSB or 1/2 in plywood; roof decking is 1/2 in or 5/8 in with H-clips between rafters.
- Nail sheathing 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 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.
How much does a sheet of plywood cover?
A 4 x 8 ft sheet covers 32 sq ft. Allow for about 10% waste from cuts, so figure about 29 usable sq ft per sheet.
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.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.