How Much Plywood for a 12x12 Shed Floor?
Sheets to buy
5 sheets
A 12 by 12 ft floor, 144 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 area12 ft
- Width or height12 ft
- What it is forSubfloor
- Framing spacing16 in on center
- Openings to deduct0 sq ft
- Waste allowance10 %
Sheets to buy5 sheets
| Gross area | 144 sq ft |
|---|---|
| Openings deducted | 0 sq ft |
| Net area | 144 sq ft |
| One sheet covers | 32 sq ft4 by 8 |
| Sheets before waste | 4.5 |
| Squares | 1.443.125 sheets per square |
| Nails per sheet | 646 in edges, 12 in field at 16 in spacing |
| Nails in total | 3203.2 lb of 8d common |
| Joist under the sheets | 108 ft |
| Subfloor adhesive | 2 tubes28 oz, about 84 ft of quarter inch bead each |
| Screws instead of nails | 4 lbsame count, number eight at about 95 to the pound |
The material list this produces
| Sheathing, 4x8 sheets | 5 |
|---|---|
| Subfloor screws, lb | 4 |
| Or 8d ring shank nails, lb | 4 |
| Subfloor adhesive, 28 oz tubes | 2 |
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
Five sheets covers 144 square feet, and the arithmetic underneath it is worth seeing: the area is exactly 4.5 sheets. Half a sheet is not a purchase, so the fifth is bought whole and half of it is spare.
Both dimensions are multiples of four here, which makes this the cleanest floor on the list to cut. Sheets laid the long way give one row of 8 ft and a 4 ft strip, and every joint falls on a four foot line, which is where the joists are anyway.
The other reason 12x12 comes up so often is the permit line. Many jurisdictions exempt a detached accessory building below a floor area threshold, and the common thresholds sit at 100, 120 and 200 square feet, so 144 is above some of them and below others. It is not a number to assume in either direction. The building department will answer it on the phone in a minute, and it is a cheaper minute than a stop work notice.
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 12x12 shed floor?
5 sheets of 4x8 plywood. The 144 square feet is exactly 4.5 sheets, and the fifth is bought whole.
Do I need a permit for a 12x12 shed?
It depends on your jurisdiction. Exemption thresholds for a detached accessory building commonly sit at 100, 120 or 200 square feet, and 144 falls above some and below others. Ask your building department rather than assuming.
Why is 12x12 easy to cut?
Both dimensions are multiples of four, so every sheet joint lands on a four foot line, which is where the joists are. Sheets laid the long way give a row of 8 ft and a clean 4 ft strip.
The plywood calculator takes any dimensions you like and hands back the same list.