Plywood Calculator
Count 4 × 8 ft or metric 2440 × 1220 sheets for a floor, wall or roof — roof areas corrected for pitch, cutting waste included.
Sheets from area — with the roof corrected
Sheet goods are the simplest count in building: area divided by sheet coverage. A 4 × 8 ft sheet covers 32 sq ft, and the metric 2440 × 1220 sheet covers 2.98 sq meters — nearly the same, which is why the two systems' counts usually agree. The one correction that matters is the roof: a pitched roof's surface is longer than the building under it, by the same slope factor the roof pitch calculator produces — a 6/12 roof has 11.8% more surface than its plan.
Sheets = plan area × slope factor × (1 + waste) ÷ sheet coverage · Slope factor = √(1 + (pitch ÷ 12)²)
Example: a 12 × 10 ft floor is 120 sq ft — 3.75 sheets on paper, so 5 sheets to buy once the 10% cutting allowance is in: sheet goods come whole, and the offcuts rarely tile a real floor.
Floors, walls, roofs — same maths, different habits
Subfloors and roof decks are laid in a staggered brick pattern with 1/8-inch gaps for expansion, which is part of what the waste allowance absorbs. Wall sheathing runs vertically or horizontally in full sheets wherever the framing allows. For roofs, measure each slope plane: a gable roof is two rectangles of eave length × slope length, and the pitch selector here does that correction from the flat plan area of both slopes combined — enter the building footprint and pick the pitch.
Thickness is a separate decision the count cannot make for you: ¾-inch for subfloors over 16-inch joist spacing, ½ to ⅝-inch for roof decks, ¼-inch underlayment under resilient floors. Match the sheet to the span rating stamped on it, not to the price tag.
Frequently asked questions
Why is my sheet count higher than area ÷ 32?
Two reasons: sheets are bought whole, and the waste allowance pays for the staggered cuts, the expansion gaps and the one sheet that always gets cut wrong. On a clean rectangle with careful layout you may land a sheet under the estimate — that sheet is your spare.
OSB or plywood — does it change the count?
No. Both come in the same sheet sizes and are counted identically; the choice between them is about moisture exposure, stiffness and price, not coverage.
How do I count a roof with two different pitches?
Figure each pitch's share of the plan area separately and add the sheets. A roof that is half 4/12 and half 8/12 cannot be averaged honestly — run the tool twice with the two plan areas.
Can I enter square meters directly?
Yes — the area field accepts sq m when the site is in metric mode, and sheet counts come out the same either way, because a metric sheet covers almost exactly a 4 × 8's area.
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