Plywood Sizes and Grades Explained
Plywood is graded on three independent axes: thickness, veneer grade, and glue durability. Understanding those three labels tells you which sheet to buy.
Thickness by use
| Thickness | Use | Why |
|---|---|---|
| 5/8" | Roof sheathing, non-load-bearing walls | Rafter spans carry the load, not the sheet |
| ¾" | Subfloor, load-bearing walls | The residential standard for floors |
| 1/2" | Over existing subfloor, walls | Fine over a solid base; too thin on its own |
| 3/8" | Second layer, shelf backs | Not structural alone |
| 1/4" | Cabinet backs, drawer bottoms | Enough to screw into, not enough to load |
Reading the stamp
Every plywood panel is stamped. The stamp gives you the manufacturer, the product name, the veneer grade, the glue exposure rating, and a number identifying the panel.
Common stamps:
- CDX — the workhorse. C grade face, D back, X for exterior glue. What you want for almost all subfloor and sheathing.
- CC — both faces C grade. Use where neither face is seen.
- BC — B grade face is sanded smooth; good where one face is painted or visible.
- AB — A grade face is the highest, sanded and defect-free. Use where the face is a finish surface.
Letters run A (best) down to D (lowest). The first letter is the face, the second is the back.
Glue exposure ratings
| Rating | Meaning | Use |
|---|---|---|
| Exterior | Bond survives full weather exposure | Any sheathing during construction, outdoor use |
| Exposure 1 | Survives limited construction delays | Roofs and walls that will be covered within weeks |
| Exposure 2 | Bond survives repeated wetting but not continuous | Fully protected interior, or interior faces of exterior panels |
| Interior | Bond fails with moisture | Dry interior applications only |
Sheathing that sits exposed to rain for weeks during a slow build needs Exposure 1 or better. Interior glue delaminating in the rain is a common and expensive mistake.
OSB versus plywood
OSB is structural sheathing — for roofs and walls only. It cannot be used where moisture is present, it is not a finish material, and it is weaker at panel edges. It is usually the right choice for subfloor under hardwood because of price.
Plywood is required where fasteners will hold significant load into the panel, where moisture is present, and anywhere the surface is seen.
MDF and particleboard
MDF machines beautifully and has a perfectly flat, uniform face — ideal for painted cabinet doors. It is heavier than plywood, sags more, and is ruined by water. Particleboard is cheaper still and only suitable for concealed, dry, low-load applications like cabinet carcasses and shop fixtures.
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