Estimate how many sheets of plywood, OSB, or other 4×8 sheet goods you need for a floor, wall, or roof area.
sheets = area ÷ 32 × (1 + waste)
A standard 4×8 sheet covers 32 ft². Divide your area by 32 and add waste for cuts.
Most plywood and OSB comes in 4×8 sheets; some specialty panels are 4×10 or 4×12.
A 16 x 20 ft room is 320 square feet. With 4 x 8 sheets (32 sq ft each), that's exactly 10 sheets with no waste — but real rooms aren't perfect multiples, so add 10% for cuts around the perimeter and you'd buy 11 sheets.
For subfloor and sheathing, stagger the sheet joints (don't line them all up) and leave a small expansion gap between sheets. That staggering is partly why the waste factor exists — the offcuts from one row don't always start the next.
A 4×8 sheet is exactly 32 ft². Adjust the coverage field for non-standard sheet sizes.
Plywood and OSB come in 4×8 sheets covering 32 square feet. Divide the surface area by 32 and round up, adding waste for cuts. On walls and roofs, running sheets so they span the framing (perpendicular to studs or rafters) ties the structure together and reduces cut joints — orientation affects waste and strength, not the raw sheet count.
Thickness is driven by span and load: ⅜–½ in for wall sheathing, ½–⅝ in for roof decking, ¾ in for subfloor. Grade (the letter pairs like CDX or sanded BC) sets the face quality and exposure rating — exterior and structural uses need an exterior-glue rating. Pick thickness and grade for the application before pricing, since both move the cost.
Divide the floor area by 32. A 320 ft² floor needs 11 sheets with 10% waste.
Divide the total surface area by 32 square feet (a 4×8 sheet) and round up, then add about 10% waste for cuts and offcuts that cannot be reused.
Roughly ⅜ to ½ inch for wall sheathing, ½ to ⅝ inch for roof decking, and ¾ inch for subfloor — the exact figure depends on the span between framing members.
Both come in 4×8 sheets and are estimated the same way. OSB is usually cheaper, while plywood resists moisture swelling slightly better at cut edges; structural ratings are comparable when rated for the same use.