How this calc works

A sheet of plywood or OSB is 4x8 — 32 square feet. This calc takes the area you are sheathing or subflooring and divides by 32, then adds waste for cuts and the offcuts you cannot reuse. The result is the sheet count to order for floors, walls, or roof decking.

Sheathing has a rhythm: stagger the joints so seams do not line up, and you generate offcuts that are too short to span but fine for filler pieces. The waste factor in this calc accounts for the pieces you cannot reuse — a clean rectangular floor wastes little, a cut-up roof with hips and valleys wastes more.

Common mistakes

The miss is ordering exact sheet count with no waste, then coming up two sheets short because the offcuts did not land where the small pieces were needed. Keep the waste factor on.

The second is buying the wrong thickness or rating — subfloor, wall sheathing, and roof decking have different thickness and exposure requirements. The sheet count is right; make sure the spec is too.

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