Plywood Calculator: How Many Sheets (4×8 or 1200×2400)
Plywood or OSB sheets to cover a floor, roof or wall, in 4 × 8 ft or 1200 × 2400 mm sheets.
Inputs
- Working
- 20 m² ÷ 2.973 m² a 4 × 8 ft sheet = 6.73, + 10% = 7.4 → 8
- Surface area
- 20 m²
- Sheet size
- 4 × 8 ft (2.973 m²)
- Without waste
- 7
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What each Plywood input means
- Surface length
- The length of the floor, wall or roof plane, in metres or feet. For a roof, use the sloped length (the run × the pitch multiplier).
- Surface width
- Its width, in the same unit.
- Sheet size
- 4 × 8 ft (32 sq ft, 2.973 m²) in North America, or 1200 × 2400 mm (2.88 m²) in metric markets — about 3% smaller.
- Waste allowance
- Extra for cuts. Panels must break over joists or rafters, so awkward dimensions waste more than the area suggests.
- Units
- Metric (metres, m², litres) or US units (feet, square feet, gallons). Lengths already typed are converted, and the sheet choice stays as it was.
Plywood formula
sheets = length × width ÷ sheet area × (1 + waste %), rounded up
Divide the area to cover by the area of one sheet, add waste for cuts and round up. In North America the standard sheet is 4 × 8 ft — 32 square feet, 2.973 m². Metric markets sell 1200 × 2400 mm sheets, which are 2.88 m², about 3% smaller; on a large floor that is enough to need an extra sheet, so choose the size you are actually buying. Plywood and OSB in the same sheet size count the same way. A roof's area is its sloped area, so work it out from the footprint and the pitch multiplier first.
Plywood worked example
A 5 × 4 m subfloor is 20 m². A 4 × 8 ft sheet covers 2.97 m², so 20 ÷ 2.97 = 6.73 sheets, 7.4 with 10% for cuts — order 8. In 1200 × 2400 mm sheets (2.88 m²) it is 6.94, or 7.64 with waste: still 8, but a slightly larger floor tips the metric count up first.
More Plywood examples
A 20 × 24 ft subfloor: 480 sq ft ÷ 32 = 15 sheets exactly, 16.5 with 10% for cuts, so 17 sheets of 4 × 8.
A 6 × 4 m shed floor in 1200 × 2400 mm sheets: 24 ÷ 2.88 = 8.33 sheets, 9.17 with 10%, so 10.
Where the Plywood calculator can give the wrong answer
- A roof's area is the sloped area: the footprint times the pitch multiplier from the roof-pitch calculator.
- Panels have to break over joists or rafters, so a layout with odd dimensions wastes more than the area suggests.
- Span ratings, thickness and grade are structural choices this does not make.
- Tongue-and-groove subfloor panels lose a little width to the joint; check the coverage on the product sheet.
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Plywood reference table
| Area | Sheets without extra | Sheets with 10% |
|---|---|---|
| 100 sq ft | 3.13 | 4 |
| 200 sq ft | 6.25 | 7 |
| 300 sq ft | 9.38 | 11 |
| 480 sq ft | 15 | 17 |
| 640 sq ft | 20 | 22 |
| 1,000 sq ft | 31.25 | 35 |
Plywood FAQ
- Area ÷ 32 sq ft for 4 × 8 sheets, plus waste. A 20 × 24 ft floor is 480 sq ft ÷ 32 = 15 sheets, 16.5 with 10% — 17 sheets.
- 32 sq ft for a 4 × 8 ft sheet, which is 2.973 m². A metric 1200 × 2400 mm sheet is 2.88 m², or 31 sq ft.
- Work out the roof's sloped area first — footprint × the pitch multiplier, 1.118 for a 6/12 roof — then divide by 32 sq ft. A 1,500 sq ft footprint at 6/12 is 1,677 sq ft of roof, 52.4 sheets, 58 with 10%.
- Yes. The sheet sizes are the same, so the count is the same; the choice between them is about the job and the code, not the arithmetic.
- 31.25 sheets exactly, since each covers 32 sq ft; with 10% for cuts, 35 sheets.
- Wall area is the perimeter times the height, less big openings. A 10 × 12 ft shed with 8 ft walls has 44 × 8 = 352 sq ft: 11 sheets of 4 × 8, or 13 with 10% for the cuts around the door and window.
- A 1200 × 2400 mm sheet is 2.88 m², while a 4 × 8 ft sheet is 1219 × 2438 mm, 2.973 m² — about 3% more. Over 30 sheets that adds up to roughly one sheet, so choose the size you are actually buying.
- Multiply the footprint, overhangs included, by the pitch multiplier: 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12. The roof-pitch calculator does it, and its area goes straight into this page.