Enter the size of the floor, wall or roof plane, any openings and the sheet size. The calculator adds waste for cuts and gives the number of plywood or OSB sheets to buy.
Plywood formula
Net area = length × width − openings Sheets = net area × (1 + waste %) ÷ sheet area, rounded up
APA notes that panels are made slightly under the nominal 48 × 96 in so they can be gapped at the edges; for estimating, a 4 × 8 sheet covers 32 sq ft.
Worked example: a 20 × 12 ft subfloor
- Area: 240 sq ft.
- With 10% waste: 264 sq ft ÷ 32 = 8.25, so 9 sheets.
Sheets by area (4 × 8, 10% waste)
| Area | Sheets |
|---|---|
| 100 sq ft | 4 |
| 200 sq ft | 7 |
| 300 sq ft | 11 |
| 500 sq ft | 18 |
| 800 sq ft | 28 |
| 1000 sq ft | 35 |
Roofs and walls
- For a roof, use the sloped area of each plane, not the footprint; the roofing calculator gives the sloped area.
- For walls, enter the total wall length and height and deduct windows and doors.
- Sheathing thickness and nailing are set by your plans and local code.
Questions
How many sheets of plywood for a 12 × 12 room?
5 sheets of 4 × 8 with 10% waste.
Is OSB calculated the same way?
Yes; OSB comes in the same sheet sizes.
How much waste for plywood?
About 10% is a common allowance; more for many angles or small pieces.
Sources
- Plywood, APA – The Engineered Wood Association.
Used for: Panels are slightly less than the nominal 48 × 96 in.