How Much Plywood for a 12x20 Shed Floor?
Sheets to buy
9 sheets
A 12 by 20 ft floor, 240 square feet, joists 16 in on center, ten percent waste.
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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.
- Length of the area20 ft
- Width or height12 ft
- What it is forSubfloor
- Framing spacing16 in on center
- Openings to deduct0 sq ft
- Waste allowance10 %
Sheets to buy9 sheets
| Gross area | 240 sq ft |
|---|---|
| Openings deducted | 0 sq ft |
| Net area | 240 sq ft |
| One sheet covers | 32 sq ft4 by 8 |
| Sheets before waste | 7.5 |
| Squares | 2.43.125 sheets per square |
| Nails per sheet | 646 in edges, 12 in field at 16 in spacing |
| Nails in total | 5765.8 lb of 8d common |
| Joist under the sheets | 180 ft |
| Subfloor adhesive | 3 tubes28 oz, about 84 ft of quarter inch bead each |
| Screws instead of nails | 7 lbsame count, number eight at about 95 to the pound |
The material list this produces
| Sheathing, 4x8 sheets | 9 |
|---|---|
| Subfloor screws, lb | 7 |
| Or 8d ring shank nails, lb | 6 |
| Subfloor adhesive, 28 oz tubes | 3 |
Floor size compared
The common twelve foot wide floors, which is the widest a shed gets before it is a building. The middle column is the area divided by a sheet, before the waste allowance.
| Floor size | Sheets to buy | Sheets before waste | Joist under the sheets |
|---|---|---|---|
| 12 by 10 ft | 5 sheets | 3.75 | 90 ft |
| 12 by 12 ft | 5 sheets | 4.5 | 108 ft |
| 12 by 14 ft | 6 sheets | 5.25 | 126 ft |
| 12 by 16 ft | 7 sheets | 6 | 144 ft |
| 12 by 20 ft | 9 sheets | 7.5 | 180 ft |
| 12 by 24 ft | 10 sheets | 9 | 216 ft |
What else matters here
Nine sheets over 180 ft of joist, and at this size the sheet count stops being the interesting number. The thickness is.
Subfloor plywood is specified against the joist spacing, not against the area, and the two are quoted together on the panel's own stamp as a span rating. Wider joist spacing needs a thicker sheet, and the usual pairing runs from about half an inch at 16 in on center for a light duty floor up to three quarters and more as the spacing opens out. The calculator holds the spacing at 16 in on center here, which is what the 180 ft of joist is counted at.
Change the spacing in the calculator and watch what moves. The sheet count does not, because the area has not changed. The joist footage does, and so do the nails and the adhesive, because those are counted along the framing rather than across the floor. That is the honest picture: wider spacing buys less joist and needs more sheet.
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
How many sheets of plywood for a 12x20 shed floor?
9 sheets of 4x8 plywood over 240 square feet, with a ten percent waste allowance.
What thickness plywood for a shed floor?
It is set by the joist spacing rather than the floor size, and the panel's span rating stamp states what it will carry. Light duty at 16 in on center is commonly half an inch, and it goes up as the spacing opens out.
Does wider joist spacing change the number of sheets?
No. The sheet count comes off the area. What changes is the joist footage, the nails and the adhesive, because those are counted along the framing.
The plywood calculator takes any dimensions you like and hands back the same list.