About this calculator
How many sheets of OSB, ply or chipboard 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
- 10 m
- Area width / height
- 2.4 m
- Openings to subtract
- 0 m²
- Sheet size
- 2440 × 1220 mm
- Material
- OSB
- Waste allowance
- 10%
the result is:
- Sheets needed
- 9 sheets
- Net area
- 24 m²
- Area purchased
- 26.79 m²
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 3 mm expansion gap the manufacturer recommends.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.