Plywood Sheet Calculator
Calculate how many sheets of plywood or OSB you need for a floor, walls, a roof or any area — with waste, sheet sizes from 2 × 4 to 4 × 10 ft or custom, a whole-sheet layout count, nails, weight and cost.
How it works
area = total area, floor length × width, wall perimeter × height − openings, or roof (length + 2 × overhang) × (width + 2 × overhang) × √(1 + (pitch ÷ 12)²) · sheets = ⌈area × (1 + waste%) ÷ sheet area⌉ · grid layout = ⌈length ÷ sheet length⌉ × ⌈width ÷ sheet width⌉ (best orientation) · nails per sheet = edges at 6 in + intermediate framing at 12 in
Divide the area by the area of one sheet — a 4 × 8 sheet is 32 sq ft — and round up after adding a waste allowance for cuts and the offcuts that do not fit elsewhere. The calculator can work out the area for you: a floor is its length times its width, walls are the perimeter times the wall height less any openings you will not sheathe, and a roof is the footprint plus the overhangs, multiplied by the pitch factor that turns the flat plan into the sloped surface (1.118 for a 6/12 roof). For a floor it also counts a whole-sheet grid with no offcuts reused, which is the most you would ever need. Nails follow the usual schedule of 6 in on panel edges and 12 in on intermediate framing, and the weight comes from typical sheet weights for the panel type and thickness, which helps with delivery and carrying.
Worked example
640 sq ft of subfloor in 4 × 8 sheets: 640 × 1.10 = 704 ÷ 32 = 22 sheets. Without waste it would be exactly 20. An 18 × 14 ft floor in Floor mode is 252 sq ft: 9 sheets with 10% waste, or 10 if you lay whole sheets in a grid without reusing offcuts (5 across the 18 ft side with the 8 ft edge along the 14 ft side, × 2). For a 6/12 roof over a 30 × 40 ft house with 1 ft overhangs, (30 + 2) × (40 + 2) = 1,344 sq ft × 1.118 = 1,503 sq ft, or 52 sheets with 10% waste.
Sources: Inch Calculator — plywood and OSB sheet weights by thickness · APA — The Engineered Wood Association, panel installation and fastening guidance
Frequently asked questions
How many square feet is a sheet of plywood?
A standard 4 × 8 sheet is 32 square feet. 4 × 9 and 4 × 10 sheets (36 and 40 sq ft) cover taller walls without a seam, and half sheets (4 × 4, 16 sq ft) and quarter sheets (2 × 4, 8 sq ft) are handy for small patches.
How many sheets of plywood do I need for a roof?
Multiply the footprint, including the overhangs, by the pitch factor: about 1.054 for 4/12, 1.118 for 6/12, 1.202 for 8/12 and 1.414 for 12/12. Divide by 32 and add 10–15% waste. A 30 × 40 ft house with 1 ft overhangs and a 6/12 roof takes about 52 sheets of 4 × 8.
Should I gap plywood sheets?
Yes — leave about 1/8 in between sheets for subfloor and sheathing so they can swell with humidity without buckling. Many tongue-and-groove subfloor panels are designed to self-gap.
How much does a sheet of plywood weigh?
A 4 × 8 sheet of 3/4 in softwood plywood weighs about 61 lb, 1/2 in about 40 lb, and OSB a little more at the same thickness. Hardwood, Baltic birch and marine plywood are heavier still. The calculator gives the weight per sheet and for the whole order.
Plywood or OSB?
OSB is cheaper and fine for most sheathing and subfloor; plywood is lighter, holds screws better and tolerates getting wet and drying out. Both come in the same sheet sizes, so the count here is identical.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.