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.
Divide the floor area by 32. A 320 ft² floor needs 11 sheets with 10% waste.