Plywood Calculator for subfloors, walls and roofs. Enter the size, sheet type, framing spacing and price to see the sheets to buy by layout, plus the cost, weight and a nail count.
Sheets are laid long side across the joists, with end joints on framing.
Framing, Panel Type and Spares
Compare Sheet Sizes
| Sheet | To Buy | Area Only | Cost |
|---|---|---|---|
| 4 × 8 ft | 11 | 9 | $495.00 |
| 4 × 9 ft | 11 | 8 | $495.00 |
| 4 × 10 ft | 9 | 7 | $405.00 |
| 4 × 12 ft | 7 | 6 | $315.00 |
| 5 × 5 ft | 16 | 12 | $720.00 |
Plywood Calculator for Subfloor, Wall and Roof Sheathing
This Plywood Calculator counts the 4 × 8 sheets a subfloor, wall or roof really takes by laying them out course by course over the framing. It is built for framers, shed and addition builders and anyone pricing a sheathing order. Along with the sheet count it gives the cost, the weight to haul and a nail count.
Pick what you are covering, then enter the length and width in feet, the sheet size, the actual panel thickness and the price per sheet. Framing spacing, panel type and spare sheets sit in the accordion. Roofs add pitch and gable or shed, and walls add the area of doors and windows.
Why the Layout Count Beats Area Divided by 32
Most plywood calculators divide the area by 32 square feet and add about 10%. That misses how sheathing actually goes down. The APA Engineered Wood Construction Guide assumes panels run with the long side across the supports and continue over two or more spans. It also puts every supported joint on the centerline of a joist, with at least 1/2 inch of bearing.
The tool follows those rules. It fills each 4 foot course along the floor, cuts each sheet end back to the nearest joist and reuses an offcut only if it still spans two joist spaces. The number of courses is the width divided by the sheet width, rounded up.
With the defaults, a 20 × 14 foot floor on 16 inch joists needs 4 courses, the last one ripped to 2 feet. The layout uses 10 sheets where area math says 9, a cut waste of 12.5%. A 5% spare rounds to 1 more sheet, so the order is 11 sheets, $495 at $45 each.
Small rooms can land right on the area figure. A 12 × 12 foot room is exactly 3 courses and takes 5 sheets either way, since 144 square feet divided by 32 already rounds up to 5.
Match Sheet Length to Your Framing
Every end joint has to land on framing, so sheet length only saves material when it divides evenly by the spacing. An 8 foot sheet works at 12, 16, 19.2 and 24 inches. A 9 foot sheet only lines up with 12 inch framing, and a 10 foot sheet with 12 or 24 inch framing.
The table runs the default 20 × 14 foot floor through the layout at three joist spacings, before spares. The Compare Sheet Sizes table in the tool does the same for your own job.
| Sheet Size | 12 in Joists | 16 in Joists | 24 in Joists | Area Only |
|---|---|---|---|---|
| 4 × 8 ft | 10 | 10 | 10 | 9 |
| 4 × 9 ft | 9 | 10 | 10 | 8 |
| 4 × 10 ft | 8 | 9 | 8 | 7 |
| 4 × 12 ft | 7 | 7 | 7 | 6 |
Walls work differently, with sheets standing on end and their long edges on studs. On a 40 foot wall 9 feet tall, 4 × 9 sheets cover each column in one piece and take 10 sheets. Using 4 × 8 sheets takes 12, and the short pieces added on top leave horizontal joints.
Those joints need blocking behind them so every panel edge can be nailed. APA's wall guidance puts supported panel joints along the centerline of framing, so plan the blocking along with the sheets.
Roof Sheathing on the Slope
For a roof, enter the length along the eave and the run per side from wall to ridge, overhang included. The slope is longer than the run, so the tool multiplies it by the pitch factor.
Here p is the rise in inches per foot of run, so a 6/12 roof has a factor of 1.118. A gable roof 30 feet long with a 14 foot run per side covers about 939 square feet of slope. Each side needs 4 courses, since the 15.65 foot slope is just under four sheet widths. On 24 inch rafters the layout takes 32 sheets where area math says 30.
The tool counts sheets for the slope only. Hips, valleys and dormers cut more waste than a plain gable, so raise the spare percentage for those roofs.
Nails, Weight and Panel Thickness
The fourth card counts nails from the fastening schedule in IRC Table R602.3(1). Subfloor sheathing gets nails 6 inches apart on supported edges and 12 inches apart at intermediate supports. The default 4 × 8 sheet on 16 inch joists takes 43 nails, about 430 for the job.
Nail size follows the panel thickness. The 2021 IRC calls for 6d common nails in 3/8 to 1/2 inch subfloor sheathing, 8d common for 19/32 to 1 inch and 10d common for 1-1/8 to 1-1/4 inch. Exterior wall sheathing has its own table, R602.3(3), where nailing depends on the design wind speed.
Roofs changed in the 2021 edition. A Simpson Strong-Tie summary notes that roof sheathing with 8d common nails now takes 6 inch spacing at intermediate supports instead of 12. Panels nailed with 10d common or 8d deformed nails keep 12 inches, and areas still on older codes enforce 12.
Panel thickness here is the actual size. The presets list 23/32 inch for panels sold as 3/4 and 15/32 for panels sold as 1/2, because those are what the tape shows.
The third card estimates weight from that thickness and a typical density for the panel type. At the defaults a sheet weighs about 61 pounds and the 11-sheet order about 675. Wet or pressure-treated panels weigh noticeably more.
For cabinet and furniture parts cut from sheets, the Plywood Cut List Calculator lays out every part. For flooring over the finished subfloor, the Plank Calculator counts boards row by row.
Sheathing Questions From the Job Site
How many sheets of plywood do I need for a 12 × 12 room?
Five 4 × 8 sheets for the floor, on either 16 or 24 inch joists. The room is 3 courses wide with no rip, and each 12 foot course takes one full sheet plus half a sheet.
The three half sheets come out of two full sheets, so the layout matches the area estimate of 144 divided by 32, rounded up. Add a spare if you want room for one bad sheet.
What size nails for a 3/4 inch plywood subfloor?
Under IRC Table R602.3(1), 23/32 inch subfloor takes 8d common nails 6 inches apart on panel edges and 12 inches apart on the joists between. That is the code minimum for nailing alone.
The APA floor installation guide recommends glue-nailing, with 6d ring- or screw-shank nails for panels in the 3/4 Performance Category or thinner. Ring or screw shanks hold better against squeaks than smooth nails.
Should there be a gap between plywood sheets?
Yes. APA recommends a 1/8 inch space at all panel end and edge joints, tongue-and-groove included, so panels can swell with moisture without buckling. APA suggests a spacer tool to keep the gap consistent.
The gap does not change the sheet count. Over a 20 foot floor, the gaps add up to well under one sheet width.