How Many Sheets of Plywood for 1,200 Square Feet?

How that number is worked out

These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.

Roof area compared

The same roof sheathing question at every common area. The middle column is squares, the unit roofing is actually sold in, and one square is a hundred square feet.

What else matters here

Forty two sheets over 12 squares of roof, and the row to look at on this page is H clips, because at the calculator's default spacing it says none and that is only true at that spacing.

An H clip is a small metal clip that sits in the gap between two sheets where the joint runs between rafters rather than over one. It holds the unsupported edge of one sheet level with its neighbour so the roof does not telegraph a ridge along every joint, and it lets a thinner panel carry the span. Set this calculator to 16 in on center and it returns none, because at that spacing the panel carries its own edge. Open the spacing to 19.2 in and it returns 210 clips, and at 24 in it returns 168.

The clip count goes down as the spacing goes up, which looks backwards until you see why: wider rafters means fewer sheet joints falling between them, but each unsupported joint is longer, so you need fewer clips holding bigger spans. That is also the point where the panel thickness has to increase, and the panel's span rating stamp is what settles it, not the clip.

What this calculator assumes

• A sheet is 4 by 8, which is 32 square feet, so three and an eighth sheets cover a square.
• Openings come off in full here, not at half. A window hole in a sheathed wall is a real hole and the offcut around it is what the waste line is for.
• The nail count is the fastener schedule rather than a rule of thumb: six inches around every edge and twelve inches into the framing in the field, so a sheet at 16 inch spacing takes 64 nails and one at 24 inch spacing takes 56. Eight penny common runs about 100 nails to the pound.
• Subfloor adhesive is figured on the linear feet of joist under the sheets, at about 84 feet of quarter inch bead from a 28 ounce tube, which is the size subfloor adhesive actually comes in.
• Roof sheathing wants H clips in each bay along the unsupported joint between rafters, which is four per sheet at 24 inches on center. At 16 inches most panel thicknesses do not need them, so the list leaves them off below 19.2 inch spacing.
• A subfloor gets screwed rather than nailed on most jobs, so the list carries the same fastener count in number eight screws at about ninety five to the pound and leaves the nail line under it as the alternative. Only one of those two lines gets bought.
• Thickness does not change the count, only the price and the span rating. Check the panel span rating against your framing spacing before you buy the thin one.

Questions people ask

Other common sizes