How many sheets of plywood do I need?
Sheets = (area − openings) × (1 + waste) ÷ sheet area, rounded up
A 20 × 12 ft floor is 240 sq ft. With 10% waste that is 264 sq ft, or 8.25 sheets of 4 × 8, so you buy 9.
Thickness by use
| Use | Typical panel |
|---|---|
| Wall sheathing | 7/16" OSB or 1/2" plywood |
| Roof sheathing, rafters 24" o.c. | 1/2" or 5/8" |
| Subfloor, joists 16" o.c. | 23/32" (3/4") tongue and groove |
| Subfloor, joists 24" o.c. | 7/8" or 1-1/8" |
| Shed floor | 3/4" tongue and groove |
Stagger the seams. On floors and roofs, run the long edge across the joists or rafters and offset end joints by at least one framing bay. Leave a 1/8" gap at panel edges for expansion.
Frequently asked questions
How many sheets of plywood for a 12x12 room?
Five 4 × 8 sheets with 10% waste (144 sq ft × 1.1 ÷ 32 = 4.95).
How many sheets for a 10x12 shed floor?
Five sheets of 4 × 8 with waste, or four if the layout lines up exactly with the joists.
Is OSB cheaper than plywood?
Usually, and it is rated for the same structural uses. Plywood handles repeated wetting and holds fasteners near edges better.