How much OSB do I need?
Enter the area and we'll work out how many OSB (sterling board) sheets you need and the cost — with the calculation shown. A standard sheet is 2.4 m × 1.2 m, so 2.88 m² each.
1 m² per m².
| OSB3 board (18mm) | 6 × 2.4×1.2 sheet | £144 |
- 1Area: 15 m²
- 2Usage rate: 1 m² per m²
- 3Allowing for waste: 15 × 1 × 1.1 waste = 17 m²
- 4Packs: 17 m² ÷ 2.88 per pack = 6 × 2.4×1.2 sheet
- Material cost only — labour is estimated separately in the schedule.
- Indicative trade-counter price; confirm with a current supplier quote.
How to work out OSB sheets
- 1Measure the area
Length × width of the floor, wall or roof deck you're boarding, in metres.
- 2Divide by sheet size
A standard OSB sheet is 2.4 m × 1.2 m = 2.88 m². So a 20 m² area needs about 20 ÷ 2.88 ≈ 7 sheets.
- 3Add ~10% for cuts
Allow for cutting around joists, openings and edges — flooring-grade tongue-and-groove boards waste a little less.
- 4Pick the thickness
18 mm is typical for flooring on standard joist spacings; thinner boards suit sheathing and hoarding. The calculator prices your board.
OSB is the workhorse board of a refurbishment — floor decks, loft boarding, sheathing and site hoarding all use it. Working from area ÷ sheet size gives the count; just match the thickness to the job, because an 18 mm floor and a 9 mm hoarding are very different boards.
OSB coverage (indicative)
| Board | Covers | Notes |
|---|---|---|
| 2.4 m × 1.2 m sheet | 2.88 m² | Standard sheet size |
| 20 m² area | ~7 sheets | Before waste |
| Flooring | 18–22 mm | T&G on standard joists |
| Sheathing / hoarding | 9–11 mm | Thinner boards |
Thickness depends on the use and the span. Add ~10% for cuts. Indicative — confirm with quotes.
Frequently asked questions
How much OSB do I need?+
Measure the area and divide by the sheet size (2.88 m² for a standard 2.4 × 1.2 m board). A 20 m² area needs about 7 sheets plus ~10% for cuts. Choose the thickness to suit the job.
What thickness of OSB for flooring?+
18 mm (often 22 mm) tongue-and-groove OSB is typical for flooring on standard joist centres. Thinner 9–11 mm boards are for sheathing, hoarding and roofing decks.
What's the difference between OSB and plywood?+
OSB (oriented strand board) is usually cheaper than plywood for the same job and fine for flooring, sheathing and hoarding. Plywood is stronger and more moisture-tolerant where that matters.
Related tools & guides
Want to know how these figures are calculated? See our cost methodology.
Cost figures shown are indicative estimates, not quotations. You are responsible for verifying all costs (obtain contractor quotes) and any figures submitted to a lender. ScopeWise is a documentation tool, not financial, tax, structural or planning advice. HMO compliance prompts are guidance only — confirm requirements with your local council, as standards and licensing vary by authority.