Plywood calculator: how many sheets of plywood do I need?
6 sheets
192 square feet to cover · 32 sq ft per sheet · for 16 × 12 ft flat
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
6 sheets
192 square feet to cover · 32 sq ft per sheet
A 12 by 16 ft floor is 192 square feet, which takes 6 sheets of 4 by 8 ft plywood, because one sheet covers 32 square feet. On a roof, the footprint is first multiplied by the pitch factor.
A worked example
A 30 by 22 ft roof footprint at a 6/12 pitch, in 4 × 8 sheets with a 5% waste allowance, needs 25 sheets. 660 square feet of footprint times the 6/12 pitch factor of 1.12 is 737.9 square feet of roof deck. With 5% for cuts that is 774.8 square feet, and at 32 square feet a sheet the count is 24.2, rounded up to 25.
How many sheets of plywood do I need for a roof?
Measure the roof footprint flat, including the overhangs, and multiply by the pitch factor: 1.05 at 4/12, 1.12 at 6/12, 1.2 at 8/12 and 1.41 at 12/12. A 30 by 40 ft footprint at 6/12 is 1,341.6 square feet of roof deck, which is 42 sheets of 4 by 8 ft before any waste allowance. Enter the footprint and the pitch above to get your own count.
What size is a sheet of plywood?
The standard sheet is 4 by 8 ft, 48 by 96 in, which is 32 square feet. It is the reference panel of PS 1-19, the U.S. product standard for structural plywood, and the standard lets a sheet measure up to 1/16 in under its stated length or width but never over. Longer 4 by 9 and 4 by 10 ft sheets are in the size selector above.
What else it is called
Plywood for a floor is sold as subfloor, and for a roof or wall as sheathing, often marked CDX. The count depends only on the sheet size, so it is the same for OSB sheets of the same dimensions. Thickness does not change how many sheets cover an area.
Common sizes
| Area | Floor or wall | Roof at 4/12 | Roof at 6/12 | Roof at 8/12 | Roof at 12/12 |
|---|---|---|---|---|---|
| 8 × 12 ft — 96 sq ft | 3 | 4 | 4 | 4 | 5 |
| 10 × 12 ft — 120 sq ft | 4 | 4 | 5 | 5 | 6 |
| 12 × 16 ft — 192 sq ft | 6 | 7 | 7 | 8 | 9 |
| 16 × 20 ft — 320 sq ft | 10 | 11 | 12 | 13 | 15 |
| 20 × 24 ft — 480 sq ft | 15 | 16 | 17 | 19 | 22 |
| 24 × 32 ft — 768 sq ft | 24 | 26 | 27 | 29 | 34 |
| 30 × 40 ft — 1,200 sq ft | 38 | 40 | 42 | 46 | 54 |
4 × 8 ft sheets, rounded up, with no waste allowance added. Roof columns use the footprint measured flat, times the pitch factor.
Where the numbers come from
- Sheets are the area divided by the square feet of the sheet you select, rounded up: a 4 by 8 ft sheet is 32 square feet. The waste allowance is yours to set.
- Sheet size: Voluntary Product Standard PS 1-19, Structural Plywood (NIST), section 5.4, which sets the 48 by 96 in panel as the reference size, and section 5.10.1, which allows a sheet to measure up to 1/16 in under its stated length or width and never over. Read October 14, 2026. PS 1-19 (PDF)
- Roof area is the footprint times the pitch factor, √(rise² + 12²) ÷ 12, which is Pythagoras: 1.05 at 4/12, 1.12 at 6/12, 1.2 at 8/12 and 1.41 at 12/12.
Measure a roof flat, from above, including the overhangs, and enter the pitch: the calculator turns the footprint into the sloped area. The count does not subtract windows, doors or skylights, and hips, valleys and gables add scrap that only your waste allowance covers.
By Javier Miralles · Last updated . How this site is made.
Other materials
Embed this calculator
Free to use on your own site. Copy the code and keep the credit line.