How many square feet is a sheet of plywood?

A standard 4 by 8 ft sheet of plywood or OSB is 32 square feet. Sheets also come in 4 by 9 and 4 by 10 for taller walls, which are 36 and 40 square feet.

What thickness of plywood for a subfloor?

Most subfloors use 3/4-inch (23/32) tongue-and-groove plywood or OSB over joists spaced 16 inches on center. Wider joist spacing or tile underlayment may call for thicker panels — check your local code.

How much waste should I add for plywood?

About 10 percent for a simple rectangular area, and 15 percent or more for rooms with lots of angles, cutouts, or a staggered layout, which create more offcuts. Round up to whole sheets either way.

Plywood Calculator — How Many 4×8 Sheets Do I Need?

Q: How many sheets of plywood do I need?

Find the area in square feet by multiplying length by width, add about 10 percent for waste, then divide by 32 — the square footage of a 4 by 8 ft sheet. Round up to the next whole sheet. A 20 by 16 ft floor (320 sq ft) needs about 11 sheets with waste included.

How many sheets of plywood do I need?

Sheet goods are estimated straight from the area you're covering:

Sheets = area × (1 + waste) ÷ coverage per sheet, rounded up

Multiply length by width for the area, add a waste allowance for cuts and offcuts, and divide by the square footage of one sheet — 32 sq ft for a standard 4 × 8. Round up, because you can't buy a partial sheet. A 20 × 16 ft room is 320 sq ft, which comes to about 11 sheets once waste is included.

Sheet sizes and thicknesses

Use	Typical panel
Subfloor	3/4 in (23/32) T&G, 32 sq ft
Wall & roof sheathing	7/16–1/2 in OSB/plywood, 32 sq ft
Tall walls	4×9 (36 sq ft) or 4×10 (40 sq ft)
Underlayment	1/4–1/2 in, 32 sq ft

Plywood vs. OSB

For subfloors and sheathing the two are largely interchangeable and code-approved. OSB costs less and comes in consistent sheets; plywood is a little lighter, holds screws better, and dries faster if it gets wet (OSB swells more at cut edges and stays swollen). For a subfloor under tile, or anywhere that may see moisture, many builders still prefer plywood.

Plywood grades, quickly

Plywood faces are graded by letter — A (smooth, sanded, paintable) down to D (knots and patches). A panel shows two letters, like BC (one good face) or CDX (C/D faces, "X" exterior glue) — CDX is the common construction/sheathing grade. Use sanded A/B grades for finished work, pressure-treated for ground contact, and marine plywood only where it'll be genuinely wet.

How much does plywood cost?

A 4×8 sheet runs about $15–$70 depending on type, thickness, and grade — OSB sheathing at the low end, sanded hardwood-faced and pressure-treated plywood much higher. Prices swing with the lumber market, so check current pricing before you budget.

Tips

Stagger the seams. Offset end joints row to row for strength — this adds a little waste, so keep 10–15%.
Leave an expansion gap. Space panels about 1/8 in so they don't buckle; tongue-and-groove edges handle this for you.
Glue and screw subfloor. Construction adhesive plus screws stops squeaks far better than nails alone.
Round up by a sheet. One spare panel is cheap insurance against a miscut.

Estimating sheets for walls and roofs

The same area-÷-32 math covers more than floors. For wall sheathing, use the gross wall area (perimeter × height) and don't bother subtracting small window and door openings — that's your waste buffer, and full sheets get cut to fit anyway. For roof sheathing, you need the sloped roof area, not the footprint: multiply the footprint by the pitch factor (about ×1.12 for a 6:12 roof) the same way the roofing calculator does, then divide by 32. In every case round up to whole sheets and keep 10–15% for offcuts and staggered seams.

Frequently asked questions

How many sheets for a 20×16 ft floor?

That's 320 sq ft. With 10% waste and 32 sq ft sheets, about 11 sheets of 4×8 plywood or OSB.

How big is a sheet of plywood?

A standard sheet is 4×8 ft = 32 sq ft. Taller 4×9 and 4×10 sheets are 36 and 40 sq ft.

What thickness for a subfloor?

Usually 3/4-inch tongue-and-groove over joists 16 in on center. Check your code for wider spacing or tile.

How much waste should I add?

10% for a simple rectangle, 15%+ for lots of angles or cutouts. Always round up to whole sheets.

Is OSB or plywood better?

Both are code-approved for subfloor and sheathing. OSB is cheaper; plywood is lighter, holds screws better, and handles moisture better — a common choice under tile or in damp areas.

What does CDX plywood mean?

C and D face grades with exterior ("X") glue — the standard, economical sheathing plywood. The glue is water-resistant, but the panel itself isn't meant for constant exposure.

What plywood do I use outside?

Pressure-treated plywood for ground contact or framing exposed to weather, and marine plywood only where it stays genuinely wet. CDX handles temporary exposure during construction.

Can I use this for wall or roof sheathing?

Yes — enter the area to cover. For walls use perimeter × height (don't subtract small openings); for roofs use the sloped area (footprint × pitch factor), then it divides by the sheet size as usual.

How do I figure plywood for a roof?

Find the sloped roof area first — footprint × the pitch factor (≈1.12 for 6:12) — then divide by 32 sq ft per sheet and add 10–15% waste. The roof pitch calculator gives the factor.