Solve backwards
How much subfloor will my plywood sheets cover?
- 20 sheetsThe example worked below
- Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof)Every figure is its own
You have
How much plywood or OSB?
Worked by the Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) at the settings below.
The settings it uses
- Waste Factor (%)
- 10
What it will do
582 sq ft of subfloor or deck
54.1 m²
One subfloor. Enough for a subfloor 20.9 × 27.9 ft.
Or several. About 1 subfloor of the size the Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) opens on: a subfloor 19.5 × 26 ft.
Check it forwards
- Area Length
- 20.9 ft
- Area Width
- 27.9 ft
- It asks for
- 20 sheets (4x8 ft)
- You have
- 20 sheets (4x8 ft)
The Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) asks for 20 sheets (4x8 ft) at that size, and 21 sheets (4x8 ft) one step larger.
If you had more, or less
Around your amount
Each worked by the Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) at the same settings.
Half
10 sheets
291 sq ft
a subfloor 14.8 × 19.7 ft
Yours
20 sheets
582 sq ft
a subfloor 20.9 × 27.9 ft
Half as much again
30 sheets
873 sq ft
a subfloor 26 × 34 ft
Double
40 sheets
1,164 sq ft
a subfloor 30 × 39 ft
Common amounts
What each amount of plywood or OSB covers
The sizes it is usually sold in, each worked by the Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) at the settings above.
| You have | It covers | As one subfloor | Average subfloors |
|---|---|---|---|
| 5 sheets | 145 sq ft(13.5 m²) | a subfloor 10.4 × 13.9 ft | under 1 |
| 10 sheets | 291 sq ft(27 m²) | a subfloor 14.8 × 19.7 ft | under 1 |
| 20 sheets | 582 sq ft(54.1 m²) | a subfloor 20.9 × 27.9 ft | 1 |
| 40 sheets | 1,164 sq ft(108 m²) | a subfloor 30 × 39 ft | 2 |
A sheet is four by eight, or near it
The calculator counts the market's standard panel: 4 by 8 feet in North America, 32 square feet or 2.97 m², and 2440 by 1220 mm in metric markets, 2.98 m². Plywood and OSB share the size, so the answer holds for either — what changes between them is the edge treatment and the span, not the count.
Ten per cent is for a simple rectangle
The waste allowance opens at ten per cent, standard for a plain rectangular area, and read backwards it comes off: twenty sheets sheath the area of about eighteen. A roof of hips and valleys, a floor full of stair openings, or a panel whose face grade must run one way leaves more offcut than that.
The gaps and the clips are extra
Most sheathing applications specify a small expansion gap between sheets, which changes how many a long run needs, and none is allowed for here. Fasteners, adhesive, blocking at unsupported edges and the H-clips some roof decks require are separate orders from the sheets.
How the answer is worked
Nothing here is a second formula. The Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof) runs forwards — a size in, a quantity out — and this page grows its own starting subfloor in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof)
runs it forwardsEstimate how many 4x8 ft (2440x1220 mm) plywood or OSB sheets you need for a subfloor, wall sheathing, or roof deck.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much subfloor or deck does 20 sheets of plywood or OSB cover?
- At the Plywood and OSB Sheet Calculator (Subfloor, Wall and Roof)'s own settings, 582 sq ft (54.1 m²) — a subfloor 20.9 × 27.9 ft. That is about 1 subfloor of the size the calculator opens on: a subfloor 19.5 × 26 ft. Every figure follows the settings, which you can change in the calculator.
- How many square feet does a sheet of plywood cover?
- A standard 4 by 8 foot sheet covers 32 square feet, 2.97 m², and a 2440 by 1220 mm metric sheet 2.98 m². With the usual ten per cent allowance for cutting, a sheet sheaths about 29 square feet (2.7 m²) of a simple rectangular area.
- Is OSB the same size as plywood?
- Yes — both are sold in the same 4 by 8 foot panels in North America and 2440 by 1220 mm in metric markets, so a sheet count works for either. They differ in edge swelling when wet, stiffness and fastener holding, which decide which to use rather than how many.
- Should subfloor sheets have a gap between them?
- Most panel makers and sheathing applications call for a small gap at the edges and ends — commonly about an eighth of an inch, 3 mm — so the panels can swell without buckling. The gap is not in the calculator's count, so a long run can need a part sheet more than the area suggests.