About this calculator
How many sheets of OSB or plywood cover a wall, roof or floor, with openings removed.
How it’s calculated
Sheets = (area − openings) × (1 + waste) ÷ sheet area.
Worked example
With these inputs:
- Area length
- 40 ft
- Area width / height
- 8 ft
- Openings to subtract
- 0 sq ft
- Sheet size
- 4 × 8 ft
- Material
- OSB
- Waste allowance
- 10%
the result is:
- Sheets needed
- 11 sheets
- Net area
- 320 sq ft
- Area purchased
- 352 sq ft
Tips from the trade
- Roofs with hips and valleys waste more: allow 12–15%.
- Stagger the end joints of sheets and land every edge on framing.
- Leave the ⅛" expansion gap the manufacturer recommends.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.