Plywood Calculator
Plywood Calculator
Work out how many sheets of plywood or OSB a floor, roof or wall needs from its size, with the roof pitch, openings and a waste allowance built in. The page gives the sheets to buy, a layout drawn to scale for floors, the weight of the stack and the cost, for 4 x 8, 4 x 9, 4 x 10 or metric sheets.
Sheet layout, to scale
Sheets by sheet size
Sheets are the area to cover divided by the area of one sheet, plus the waste allowance, rounded up. Roofs are measured by their plan footprint and multiplied by the pitch factor, the length of a sloping rafter per foot of run: 1.054 for 4/12, 1.118 for 6/12 and 1.202 for 8/12. Openings are taken off walls and other areas. For floors given by length and width, the page also works out the whole sheet layout both ways round. Weights assume about 34 lb per cubic foot for softwood plywood and 40 for OSB; they vary with species, glue and moisture. Nominal 1/2, 5/8 and 3/4 in panels are usually 15/32, 19/32 and 23/32 in thick. The CSV, image and printed report contain the values you entered, nothing preloaded.
How to use this tool
Choose the job: a floor or subfloor, roof sheathing, wall sheathing or any other area. Enter the length and width, or the area directly; for a roof, enter the plan footprint and pick the pitch, and for walls enter the total wall length and height and the area of windows and doors to take off. Pick the sheet size, material and thickness, and the sheets to buy appear at the top with the weight of the stack.
For floors the drawing lays the sheets out to scale in staggered rows, the way they go down on the joists. The chart compares sheet sizes for the same job, and the table gives the weight of every common thickness.
How the sheets are counted
A 4 x 8 ft sheet covers 32 sq ft. The area to cover divided by 32 is the exact number of sheets; adding a waste allowance, 10 percent by default, and rounding up gives the number to buy. Openings in walls come off first.
Roofs are measured on plan, which is easy to do from the ground or a drawing, and then multiplied by the pitch factor: the length of a rafter for every foot of horizontal run. At 6/12 pitch the roof rises 6 in per foot and the factor is the square root of 1 plus 0.5 squared, 1.118, so the deck is 11.8 percent bigger than the footprint.
Sheets for common floors
| Floor | Area | Sheets exact | Buy, with 10% | Whole sheet layout |
|---|---|---|---|---|
| 8 x 12 ft | 96 sq ft | 3 | 4 | 3 |
| 10 x 10 ft | 100 sq ft | 3.13 | 4 | 6 |
| 10 x 12 ft | 120 sq ft | 3.75 | 5 | 6 |
| 12 x 12 ft | 144 sq ft | 4.5 | 5 | 6 |
| 12 x 16 ft | 192 sq ft | 6 | 7 | 6 |
| 16 x 20 ft | 320 sq ft | 10 | 11 | 10 |
| 20 x 20 ft | 400 sq ft | 12.5 | 14 | 15 |
| 24 x 24 ft | 576 sq ft | 18 | 20 | 18 |
4 x 8 ft sheets. The whole sheet layout counts every sheet a row starts, without reusing offcuts; staggered rows usually reuse them, so the area figure is the one to buy.
Roof sheathing by pitch
| Pitch | Factor | 1,000 sq ft footprint | 1,500 sq ft | 2,000 sq ft |
|---|---|---|---|---|
| 3/12 | 1.031 | 36 | 54 | 71 |
| 4/12 | 1.054 | 37 | 55 | 73 |
| 5/12 | 1.083 | 38 | 56 | 75 |
| 6/12 | 1.118 | 39 | 58 | 77 |
| 7/12 | 1.158 | 40 | 60 | 80 |
| 8/12 | 1.202 | 42 | 62 | 83 |
| 9/12 | 1.250 | 43 | 65 | 86 |
| 10/12 | 1.302 | 45 | 68 | 90 |
| 12/12 | 1.414 | 49 | 73 | 98 |
Sheets of 4 x 8 ft with 10 percent waste. Add more for hips, valleys, dormers and overhangs.
A worked example you can check on paper
A shed floor is 12 by 16 ft, 192 sq ft. Divided by 32 that is exactly 6 sheets of 4 x 8, and with 10 percent for mistakes, 6.6, so buy 7. Laid with the long edges across the joists, three rows of two sheets cover it, the middle row starting with a half sheet so the end joints are staggered. In 3/4 in plywood at about 65 lb a sheet, the stack weighs roughly 456 lb.
The roof over it has a 12 by 16 ft footprint at 6/12 pitch. 192 times 1.118 is 214.7 sq ft of deck, 6.7 sheets, and with 10 percent, 7.4, so 8 sheets of 7/16 in OSB before overhangs.
Choosing a thickness
Structural panels carry a span rating stamp such as 24/16, which gives the widest rafter spacing and floor joist spacing the panel is rated for, and building codes set the minimum for each job. As common practice, walls and roofs on framing at 16 or 24 in centers are often sheathed with 7/16 in OSB or 15/32 in plywood, and floors use 23/32 in tongue and groove panels. Thinner 1/4 and 3/8 in sheets are for underlayment, paneling and non structural work.
Mistakes that catch people out
Using the footprint for a roof. Multiply by the pitch factor, or a steep roof will be short by a fifth or more.
Running floor sheets the wrong way. The long edge goes across the joists, with end joints staggered and landing on a joist.
Butting sheets tight. Leave the gap the maker asks for, usually 1/8 in at edges and ends, or the sheets can buckle when they swell.
Ignoring the weight. A stack of 3/4 in plywood is heavy; check what a truck, trailer or upper floor can carry.
Buying exactly the count. Cuts, damaged corners and mistakes happen. The waste allowance is cheaper than a second trip.
Popular calculations
Each opens the calculator with its own address, and every value can be changed once it is open.
Floors and subfloors
Any area
Roof sheathing
Walls and metric
How this was checked
The engine was tested in Node against hand calculations: a 12 by 16 ft floor is exactly 6 sheets of 4 x 8 and 7 with 10 percent; a 1,500 sq ft footprint at 6/12 is 1,677.1 sq ft of deck, 52.41 sheets and 58 with waste; 800 sq ft of wall less 80 sq ft of openings is 720 sq ft, 22.5 sheets and 25 to buy; and a 1200 x 2400 mm sheet covers 2.88 m². Pitch factors were checked against the square root of 1 plus the rise over 12 squared, and sheet weights against thickness times 32 sq ft times density.
Every address in the lists above was then opened and checked for a distinct title, the right answer, drawings that render, and clean CSV, image and print output containing only that calculation, at desktop, tablet and phone widths.
Common questions
How many sheets of plywood do I need for a 12 by 16 floor?
The floor is 192 sq ft, and a 4 x 8 sheet covers 32 sq ft, so it takes exactly 6 sheets. With 10 percent for cuts and mistakes, buy 7. Laid out whole, three rows of two sheets cover it, so the seventh is a spare.
How many square feet does a sheet of plywood cover?
A 4 x 8 ft sheet covers 32 sq ft, a 4 x 9 covers 36 and a 4 x 10 covers 40. A metric 1200 x 2400 mm sheet covers 2.88 m², about 31 sq ft.
How do I work out plywood for a roof?
Measure the plan footprint of the roof, multiply by the pitch factor to get the sloping area, divide by 32 and add about 10 percent. A 1,500 sq ft footprint at 6/12 pitch is 1,677 sq ft of deck, 52.4 sheets, so buy 58.
How much does a sheet of 3/4 plywood weigh?
A 4 x 8 sheet of 23/32 in softwood plywood weighs roughly 60 to 70 lb, about 65 lb at a typical density. A sheet of 7/16 in OSB is about 45 to 50 lb. Hardwood and marine plywood are heavier.
Should I use plywood or OSB?
Both are rated structural panels, and a panel with the same span rating can be used for the same job. OSB is usually cheaper and very uniform but swells at the edges if it stays wet; plywood is a little lighter and recovers better from getting wet. Check the stamp either way.
How much extra plywood should I buy?
About 10 percent for simple rectangles, 15 percent or more for roofs with hips, valleys and dormers or walls with many windows and doors. Leftover sheets are always useful, and a short order stops the job.
Related Calculators and Reference
- Roof Squares Calculator: roofing squares and shingles for the same roof.
- Deck Material Calculator: joists, boards and fasteners for a deck.
- Drywall Calculator: sheets, tape and compound for the inside of the walls.
- Board Foot Calculator: lumber for the framing.
- Square Footage Calculator: for floors and walls that are not simple rectangles.
- APA, The Engineered Wood Association: plywood grades, span ratings and panel standards.