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Plywood Thickness Chart
Quick answer: Structural panels run 1/32″ under nominal. “1/2″” sheathing is 15/32″ and “3/4″” subfloor is 23/32″. Cabinet-grade hardwood plywood is often closer to true nominal.
Actual thickness for every nominal sheet size, what the span rating stamp means, and the difference between plywood and OSB where it actually matters.
Plywood and sheet goods thickness chart
Structural panels are sold under a nominal name and manufactured to a different actual thickness. The difference is small — usually 1/32″ — and it matters exactly when you are cutting a dado, setting a router depth, or matching a panel edge to dimensional lumber.
| Nominal | Actual | Metric | Common use |
|---|---|---|---|
| 1/4" | 0.250" | 6.4 mm | Underlayment, cabinet backs |
| 3/8" | 0.375" | 9.5 mm | Wall sheathing (older), soffit |
| 15/32" | 0.469" | 11.9 mm | Nominal 1/2" wall sheathing |
| 1/2" | 0.500" | 12.7 mm | Drywall, cabinet sides |
| 19/32" | 0.594" | 15.1 mm | Nominal 5/8" roof sheathing |
| 5/8" | 0.625" | 15.9 mm | Type X drywall, roof deck |
| 23/32" | 0.719" | 18.3 mm | Nominal 3/4" subfloor (T&G) |
| 3/4" | 0.750" | 19.1 mm | Cabinet-grade ply, shelving |
Why structural panels are undersized
Structural plywood and OSB are made to a performance standard rather than a dimensional one. PS 2 rates a panel by what it can span and carry, not by what it measures — so mills produce to a thickness that meets the rating with the least material. Cabinet-grade hardwood plywood follows a different tradition and often runs closer to its nominal size, which is why the same 3/4″ setting works for one sheet and not another.
Span ratings
The stamp on a structural panel carries two numbers, like 32/16. The first is the maximum roof support spacing in inches; the second is the maximum floor joist spacing. A 32/16 panel spans 32″ on a roof and 16″ on a floor.
| Span rating | Typical thickness | Roof spacing | Floor spacing |
|---|---|---|---|
| 24/0 | 3/8″ | 24″ | Not rated for floor |
| 24/16 | 7/16″ | 24″ | 16″ |
| 32/16 | 15/32″ | 32″ | 16″ |
| 40/20 | 19/32″ | 40″ | 20″ |
| 48/24 | 23/32″ | 48″ | 24″ |
Plywood vs OSB
| Plywood | OSB | |
|---|---|---|
| Structure | Cross-laminated veneers | Compressed oriented strands |
| Cost | Higher | Lower |
| Wet performance | Dries out, regains most strength | Swells at edges, does not fully recover |
| Fastener holding | Better | Adequate |
| Weight (4x8, 23/32″) | ~61 lb | ~78 lb |
For sheathing that will be dried in quickly, OSB is the economical choice and code treats the two as equivalent at the same span rating. For anything that may sit exposed to weather, or any application where edge swelling would telegraph through a finish, plywood earns its premium.
Grades
Plywood grades are given as two letters, one per face — A-C means an A-grade front and a C-grade back. A is sanded and defect-free, B allows tight knots and small repairs, C allows knotholes up to 1″, D allows larger ones. Add X (as in CDX) and the glue is exterior-rated, which describes the adhesive, not the veneer — CDX is sheathing, not siding.
Frequently asked questions
Is 3/4 inch plywood actually 3/4 inch?
Usually not. Structural 3/4 in plywood and OSB are typically 23/32 in (0.719 in). Cabinet-grade hardwood plywood often runs closer to true 3/4 in, so measure the specific sheet before cutting a joint to fit.
What thickness is 1/2 inch plywood really?
Most so-called 1/2 in structural sheathing is 15/32 in (0.469 in). The 1/32 in difference is enough to leave a visible step where a panel meets 1/2 in drywall or a dimensional lumber edge.
What does CDX plywood mean?
C-grade face, D-grade back, exterior glue. The X refers to the adhesive, not the veneer quality — CDX will survive getting rained on during construction but is not a finished exterior product.
What does a 32/16 span rating mean?
The panel can span 32 inches between roof supports or 16 inches between floor joists. The first number is roof spacing, the second is floor spacing, both in inches.