How this calculator works
A 4 × 8 ft sheet covers 32 square feet, so the quickest estimate is the area to cover divided by 32, plus a margin for cuts. That works well for large areas where cutoffs are reused. For a rectangle, you can also count the sheets that fit in a grid: how many sheets run along the length, and how many across the width, then round up each. The calculator tries the sheets both ways round and takes the better one.
Worked example: a 16 × 12 ft floor is 192 ft², which is 6 sheets of 4 × 8 ft. With 10% waste it is 6.6, so 7 sheets. In a grid, 16 ft is two sheet lengths, and 12 ft is three widths, so 2 × 3 = 6 whole sheets fit exactly with nothing left over.
Sheets of 4 × 8 plywood by floor or roof size
Area method with 10% waste, and the whole-sheet grid. Use the larger if you cannot reuse cutoffs.
| Size | Area | By area | Grid layout |
|---|---|---|---|
| 8 × 8 ft | 64 ft² | 3 | 2 |
| 10 × 12 ft | 120 ft² | 5 | 6 |
| 12 × 12 ft | 144 ft² | 5 | 6 |
| 12 × 16 ft | 192 ft² | 7 | 6 |
| 16 × 20 ft | 320 ft² | 11 | 10 |
| 20 × 24 ft | 480 ft² | 17 | 15 |
Tips before you buy
- Check the stamp on the panel for its span rating and exposure, and match it to the joist or rafter spacing. A thicker panel is needed for a wider spacing.
- Stagger the end joints of neighboring rows, so that the seams do not line up. Leave a 1/8 in gap around each panel, to let it expand with moisture.
- Lay the long side of the sheet across the framing, with the ends landing on joists or rafters, not between them.
- For a subfloor, tongue-and-groove panels interlock along the long edges and make a stiffer floor. Glue and screw rather than nail, to avoid squeaks.
- Keep the sheets dry and flat, on stickers or a pallet, until they are used. A warped sheet is hard to nail down flat.
- OSB and plywood are sold in the same sizes, so the same count applies. They differ in how they handle getting wet and in price.
Tools & materials for this project
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Frequently asked questions
How many sheets of plywood do I need for a 12x12 floor?
Divide 144 ft² by 32 ft² to get 4.5, so 5 sheets of 4 × 8 ft, which is still 5 with 10% waste (4.95). If you cannot reuse the cutoffs, a whole-sheet grid takes 6 sheets: two along each 12 ft side, and three across.
How many square feet is a sheet of plywood?
A 4 × 8 ft sheet is 32 ft². A 4 × 10 sheet is 40 ft² and a 4 × 12 sheet is 48 ft².
How many sheets of plywood for a roof?
Use the area of the roof, not of the floor: it is larger by the slope factor (a 6/12 pitch is 12% larger). The roofing calculator gives the roof area, and you divide it by 32 and add waste.
Is it OK to use half sheets?
Yes, but they should still land on framing. Cut panels so that their edges fall on a joist or stud, or add blocking beneath the edge.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.