Plywood Subfloor Calculator
Sheets, screws, and adhesive for a plywood or OSB subfloor.
10% for rectangles, 15% for rooms with angles and jogs.
You need
14 sheets
Waste included. Stagger end joints and leave a 1/8 in gap at panel ends.
- Subfloor screws
- 490 screws
- Adhesive (28 oz tubes)
- 5 tubes
- Floor area
- 384 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Sheets = area x (1 + waste) / 32 sq ft per 4x8 sheet, rounded up. Screws assume about 35 per sheet (6 in edges, 12 in field on 16 in joists). Adhesive assumes one 28 oz tube per 3 sheets.
Enter the floor dimensions and this calculator counts the 4 x 8 sheets (32 square feet each) of plywood or OSB, plus the screws and construction adhesive that make a subfloor solid and squeak-free. The math is the same for tongue-and-groove subfloor panels, sheathing, and underlayment; only the thickness and grade change.
Sheets should run perpendicular to the joists with end joints staggered between rows, which is where the waste factor goes: end cuts, notches around corners, and the partial sheets that finish each row. 10% covers a rectangular room; add more for rooms with jogs, angles, or many penetrations.
Sheets for common floor sizes
Rows assume 4 x 8 sheets with 10% waste, screws at 35 per sheet, and one adhesive tube per 3 sheets.
| Floor size | Sheets | Screws |
|---|---|---|
| 12 x 12 ft room | 5 sheets | 175 screws |
| 16 x 12 ft room | 7 sheets | 245 screws |
| 24 x 16 ft addition | 14 sheets | 490 screws |
| 24 x 24 ft garage loft | 20 sheets | 700 screws |
| 40 x 28 ft full story | 39 sheets | 1,365 screws |
Matching panels to your joist spacing
The span rating stamped on every structural panel is what decides whether it suits your floor, and it is printed precisely so you do not have to reason from thickness. Sheathing panels carry a pair of numbers such as 32/16: the first is the maximum roof support spacing, the second the maximum floor spacing, both in inches. Sturd-I-Floor panels carry a single figure like 20 oc or 24 oc and are manufactured for this application specifically.
Read the stamp against the spacing you measured, not against a thickness someone quoted you. Framing is not always what the plans say, particularly in older houses and additions, and a panel that spans comfortably at one spacing will deflect at the next one up. Measure between three or four joists before you buy; if the spacing is irregular, size for the widest gap you found.
Sheet size affects the count more than people expect. This calculator assumes standard 4 x 8 panels because they are what most suppliers stock and what fits in a pickup, but 4 x 9 and 4 x 12 panels exist and reduce the number of seams on a large floor. If you buy a different size, divide your floor area by that panel area instead of relying on the sheet figure above.
Plywood or OSB?
At the same span rating these are structurally equivalent, and building codes treat them identically. OSB is usually cheaper per sheet and more uniform in thickness; plywood is lighter to carry, and it tolerates a soaking better because it dries out with less permanent distortion. If your deck will sit open to weather for a while, that difference is worth paying for. If it will be dried in within days, OSB does the same job for less.
The gap shows up with sustained moisture rather than a single rain. OSB swells at cut edges when it stays wet and does not fully return to its original thickness, which can telegraph through thin finish flooring as a ridge along each seam. Panels sold with a moisture-resistant edge seal are worth the small premium in either material, and covering the deck when rain is forecast costs nothing at all.
Reading the screw and adhesive figures above
The screw count assumes the standard fastening schedule for a glued subfloor, which works out to roughly 35 screws per 4 x 8 sheet. Buy coarse-thread subfloor screws in that quantity plus a margin, since a handful will strip or snap. Drywall screws are not a substitute at any price: they are hardened and brittle, and they shear under the flexing a floor sees.
The adhesive figure works out to about one 28 ounce tube per three sheets, which is what a normal bead along each joist consumes. Buy a couple of tubes beyond the number shown. Adhesive skins over if the job stops partway, and running out mid-floor means either waiting on a store run with panels half set or leaving a section unglued, which is exactly where a squeak starts.
Both figures are per the area you entered, so if you are decking a floor in stages, run the calculator for each stage rather than buying everything at once. For the full step-by-step on sheet layout and gapping, see our guide on how many sheets of plywood a subfloor takes.
Common questions
How many sheets of plywood do I need?
Divide the floor area by 32 square feet, the coverage of one 4 x 8 sheet, then add about 10% for cutting waste and round up. A 12 x 12 room is 144 square feet, so 144 / 32 = 4.5 sheets, which rounds to 5 after waste. The calculator above runs any floor size and adds the subfloor screws and construction adhesive to fasten the sheets down.
What thickness of subfloor plywood do I need?
With joists at 16 inches on center, 3/4 inch tongue-and-groove plywood or OSB is the standard for a floor that will carry tile or hardwood; 23/32 OSB subfloor panels are the common commodity version. Wider joist spacing or stone tile calls for thicker panels or an added underlayment layer.
Should I glue the subfloor down?
Yes. A bead of construction adhesive on every joist plus screws is the glued-and-screwed standard that prevents squeaks, stiffens the floor, and is required by many flooring warranties. One 28 oz tube covers roughly 3 sheets' worth of joist lines.
Screws or nails for subfloor?
Screws hold far better against the wood movement that causes squeaks. Use subfloor-rated screws about 6 inches apart on panel edges and 12 inches in the field, roughly 35 per sheet on 16 inch joists. Ring-shank nails are acceptable with adhesive, but smooth nails work loose.
Which way do subfloor sheets run?
Long dimension perpendicular to the joists, with the tongue-and-groove edges meeting between joists and end joints landing on a joist, staggered half a sheet between rows. Leave a 1/8 inch gap at panel ends per APA guidance; panels swell slightly with humidity.
Is OSB or plywood better for a subfloor?
At the same span rating they are structurally equivalent and codes treat them the same. OSB usually costs less; plywood is lighter and tolerates getting wet better, drying out with less permanent swelling. If the deck will sit open to weather choose plywood, and if it will be dried in quickly OSB does the same job for less money. Either way, look for a moisture-resistant edge seal.
Do I need underlayment over the subfloor?
Only for finishes that demand a flawless surface. Sheet vinyl and some tile installations want a thin underlayment panel or cement board over the structural subfloor. Nail-down hardwood, engineered flooring, and carpet go directly over a sound 3/4 inch subfloor with nothing between but the required underlayment paper or pad. Adding a layer you do not need costs money and raises the floor height at every doorway.
How do I fix a squeaky subfloor?
A squeak is almost always a panel moving against a fastener. From below, drive a screw up through the joist into the subfloor near the noise, or add a shim with construction adhesive where the panel has lifted off the joist. From above, drive a coarse-thread screw through the finish floor into the joist. Fixing it before the finish floor goes down is far easier, which is the argument for gluing every panel the first time.