Plywood Calculator
How many sheets of plywood or OSB cover a floor, a wall or a pitched roof, with openings taken off and the roof slope allowed for.
Result
Buy 6 sheetsEstimate
Counted by area, rounded up to whole sheetsNo extra is added by default. Cuts at hips, valleys and around openings can need more sheets.
- Area to cover
- 192 ft²
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Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Plywood Calculator
- Choose a floor, wall or ceiling, or roof sheathing.
- Enter the length and width. For a roof, use the building footprint with the overhangs, and give the pitch as rise per 12 or as an angle.
- Take off any openings that will not be sheathed, and enter the sheet size you are buying.
- Read the sheets to buy and the area they cover.
How it is calculated
roof slope factor = √(1 + (rise ÷ 12)²) roof mode onlyarea to cover = length × width × slope factor − openingssheets = ⌈area × (1 + allowance) ÷ (sheet length × sheet width)⌉The slope factor is the same one the roof area calculator uses, so both pages agree on the roof’s size. A hip roof and a gable roof over the same footprint at the same pitch have the same area.
Counting by area
Sheets are counted from the area, not from a cutting plan, so every offcut is assumed to be usable somewhere. On a plain rectangular floor that is close to true. On a roof with hips, valleys and short courses, or a wall with many openings, it is not, and the Custom allowance is where that goes. When the sheet count matters, sketch the layout: courses run with the long edge across the joists or rafters, and end joints are usually staggered, which is where offcuts get used.
With your numbers
- Area to cover = 16 ft × 12 ft − 0 ft² = 192 ft²
- Sheets = ⌈192 ft² × (1 + 0%) ÷ 32 ft²⌉ = 6
Quick reference
No extra is added by default. Cuts at hips, valleys and around openings can need more sheets.
| Job | Sheets to buy |
|---|---|
| 12 × 16 ft floor | 6 |
| 40 × 8 ft wall, 60 ft² openings | 9 |
| 40 × 28 ft roof at 6/12 | 40 |
| 40 × 28 ft roof at 12/12 | 50 |
| 24 × 24 ft garage roof at 4/12 | 19 |
| 5 × 4 m floor | 7 |
| 10 × 8 m roof at 30° | 32 |
Common questions about the Plywood Calculator
- How many 4 × 8 sheets of plywood do I need for a 12 × 16 foot floor?
- 6. The floor is 192 square feet and a 4 × 8 sheet is 32, which divides exactly. A room whose sides are not multiples of the sheet leaves offcuts, and the count assumes you can use them elsewhere on the same job.
- How does the roof mode work?
- A pitched roof has more surface than the ground it covers. The footprint is multiplied by the slope factor, the square root of 1 plus the rise over the run squared. At 6 in 12 that is 1.118, so a 40 × 28 foot footprint has about 1,252 square feet of roof, whether it is a gable or a hip at that pitch.
- Should I add extra for waste?
- The page adds none unless you choose Custom. Hips and valleys, dormers and a sheet layout that has to stagger its joints all produce offcuts too small to reuse, so choose an allowance that fits your roof or floor.
- Does this tell me what thickness to use?
- No. Thickness, grade, span rating and fastening depend on the joist or rafter spacing, the loads and local codes. Check the panel markings and your plans.