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 SANS 10400 (the National Building Regulations) and your local municipality before ordering.