How many sheets of plywood?
A 4' x 8' panel covers 32 sq ft, so area ÷ 32 is the minimum. In practice the panels are laid with the long edge across the joists or rafters and the end joints staggered by at least one framing bay, so you cut panels at the ends of rows. The calculator lays them out row by row, reusing offcuts 2 feet or longer to start the next row.
Example: a 24' x 16' subfloor is 384 sq ft — 12 sheets on paper. Laid out with staggered joints it uses 12 full sheets plus offcuts; with 5% extra, buy 13.
Which panel?
- Subfloor: 23/32" tongue-and-groove plywood or OSB rated for floors, glued and nailed or screwed to the joists.
- Roof deck: 7/16" or 1/2" OSB or plywood on rafters 24" apart, with H-clips between rafters at the panel edges.
- Walls: 7/16" OSB or 1/2" plywood, usually installed vertically or horizontally per the bracing design.
Every panel is stamped with a span rating; make sure it matches your framing spacing. Leave a 1/8" gap at panel edges and ends so they can expand.
Framing the walls first? Try the wall framing calculator. Shingling the roof? Use the roofing calculator.