Calculate how many sheets of plywood or OSB you need to cover a floor, wall or roof area, including a waste allowance.
Enter the length and width of the area you want to cover — floor, wall or roof — and pick the sheet size (or enter a custom one). The tool works out how many sheets you need with a waste allowance. It works for plywood, OSB, MDF and chipboard (“particle board”).
| Size | Region |
|---|---|
| 8 × 4 ft | US / UK common |
| 2440 × 1220 mm | Metric equivalent |
| Sheet area | 32 ft² / 2.98 m² |
A floor 20 ft × 12 ft = 240 ft². Each 8 × 4 ft sheet covers 32 ft², so 240 ÷ 32 = 7.5 → 8 sheets. Add 10% for cuts ≈ 9 sheets.
Tip: stagger the joints (like brickwork) and leave a small expansion gap of about 2–3 mm between sheets so they do not buckle as they take up moisture.
In the UK and US the standard sheet is 8 × 4 ft (2440 × 1220 mm), giving about 2.98 m² (32 sq ft) per sheet.
For a simple rectangular floor 10% is usually enough. For roofs, walls with openings or complex shapes, allow 15%.
Yes. It works for any sheet material — plywood, OSB, chipboard flooring or sheathing — as long as you use the correct sheet size.
18 mm is common for flooring, 12–18 mm for roof decking and 9–12 mm for wall sheathing. Thicker sheets span further between joists or studs.
Plywood is made from thin wood veneers glued in layers, while OSB is compressed wood strands. Plywood is stronger and copes better with moisture; OSB is cheaper and common for sheathing and decking.
