OSB board calculator

1. Area with waste = area + cutting waste (10% by default).
2. Board area = length × width (for example 2.50 × 1.25 m = 3.125 m²).
3. Boards = area with waste ÷ board area, rounded up.

For 30 m² with 10% waste you need 33 m² of OSB. With 2500 × 1250 mm boards (3.125 m²): 33 ÷ 3.125 = 10.6, so 11 boards.

• Common sizes are 2500 × 1250, 2800 × 1200 and 2440 × 1220 mm (8 × 4 ft) — choose the one that matches the joist or stud spacing so joints land on a support.
• 10% covers edge cuts and staggered joints.

• Thickness depends on use: 10–12 mm for walls and roof sheathing, 18–22 mm for floors on joists.
• In damp areas or outdoors use OSB/3 and leave 2–3 mm between boards for expansion.

Choose the grade for the conditions: OSB/3 is the usual load-bearing board for humid conditions such as roof decks, walls and subfloors; OSB/2 is for dry interiors only. Lay boards with the strong axis (marked on the board) across the supports.

Leave a 2–3 mm gap between boards and about 10 mm at walls for expansion, and stagger the end joints. Fix with ring-shank nails or screws at the spacing the manufacturer gives (often about 15 cm at edges and 30 cm in the field). Tongue-and-groove boards on floors should be glued in the joints and on the joists to stop squeaks.