Plywood Calculator (Metric)
Find how many 4x8 sheets of plywood or OSB you need to cover a surface, including a waste margin for cuts.
What your result means
Sheets needed is how many standard 4x8 plywood or OSB panels (3 m² each) cover your surface, after adding a waste margin and rounding up. Surface area is the raw area; with waste margin is what you actually plan for. Real layouts always need extra for cuts, so don't skip the margin. Buying lumber too? See our board foot calculator.
How to use this calculator
- Measure the surface length and width in feet.
- Set a waste margin — 10% for simple layouts, 15%+ for cut-heavy ones.
- Read the number of 4x8 sheets to buy.
- Buy a full extra sheet if your layout has many small pieces.
- For walls with openings, you can subtract large windows and doors.
The formula
A 4x8 sheet covers 3 m². Divide your waste-adjusted area by 32 and round up, since you can only buy whole sheets. The waste margin covers cuts and offcuts you can't reuse.
Worked example
A 20 by 4.9 m floor is 29.7 m². Add a 10% waste margin and you're planning for 32.7 m². At 3 m² per sheet that's 11 sheets of plywood.
Plywood sheet coverage
| Sheet size | Coverage | Common use |
|---|---|---|
| 4 × 2.4 m | 3 m² | Standard — floors, walls, roofs |
| 4 × 1.2 m | 1.5 m² | Easier handling, more seams |
| Subfloor | 3 m² | 3/10.2 cm T&G typical |
| Wall sheathing | 3 m² | 7/40.6 cm OSB common |
| Roof sheathing | 3 m² | 1/2 - 5/20.3 cm |
Tips & gotchas
- Buy at least one extra sheet — you'll always mis-cut or find a damaged one.
- Cut-heavy or angled layouts waste more; bump the margin to 15-20%.
- Stagger seams and orient sheets to span joists or studs for strength.
- Tongue-and-groove subfloor reduces squeaks but costs a bit more.
- OSB is cheaper than plywood for sheathing; plywood handles moisture better.
Frequently asked questions
How many sheets of plywood do I need?
Divide the surface area by 32 (a 4x8 sheet) after adding a waste margin, then round up. A 29.7 m² floor at 10% waste needs 11 sheets.
How many square feet is a sheet of plywood?
A standard 4 by 8 foot sheet covers 3 m².
How much waste should I add for plywood?
10% for simple rectangular layouts; 15 to 20% for jobs with many cuts, angles, or openings.
Is OSB or plywood better?
OSB is cheaper and fine for most sheathing and subfloor. Plywood is stiffer and handles moisture and repeated wetting better.
Can I subtract windows and doors?
For wall sheathing you can deduct large openings, but keep a margin — small offcuts around openings often aren't reusable.
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Estimates only — see our full disclaimer.