Walk into any lumber yard and the plywood section is a confusing alphabet soup. A/C, BB/CC, AB, marine, sanded, shop, premium - every yard uses slightly different conventions, and the difference between an A face and a C face can be $20 per sheet. Here's a clear guide to what the letters actually mean and which grade to buy for which job.
The system in 30 seconds
In North America, plywood is graded face-by-face with a letter (A through D, sometimes N for premium). The grade tells you about the front face quality - knots, patches, voids, color matching, and finish smoothness. Most plywood gets two grades, one per face, listed front/back like A/C - meaning A face on the front, C face on the back.
In Europe, the system uses double letters (BB/CC) and tracks slightly different criteria, but the principle is the same: the higher the letter on the alphabet, the rougher the face.
Grade-by-grade
Grade A (or AA): Smooth, paintable, very few defects. Knots are filled or absent. Small repairs are color-matched and rounded. This is what you buy for visible cabinet doors, painted shelves, and any face that gets a finish-grade clear coat. Expect to pay $60-90 per 4×8 sheet of cabinet-grade A/A.
Grade B (BB): Solid, smooth surface, but some color-matched putty repairs visible. Small knots up to 25mm allowed if they're tight (won't fall out). Acceptable for paint-grade work and any surface that won't be inspected up close. Often the right buy for cabinet interiors.
Grade C: Tight knots up to 38mm allowed. Some discoloration. Splits up to 6mm wide allowed if they're not through the panel. Suitable for sheathing, subfloor, and any structural surface that won't be visible after the build.
Grade D: Knots up to 64mm allowed, knotholes up to 38mm allowed. Heavy splits, discoloration, and patch repairs. This is the cheapest face you can buy without going to "shop grade" (the rejected stuff). Use it for paint-grade exteriors of subfloors and shop cabinets where you don't care.
Grade N: Premium "natural" face. No defects, color-matched grain, often book-matched. Used for high-end cabinet work and architectural panels. Two to three times the price of grade A.
Two-letter combos
Most plywood is sold with two grades because most plywood has different priorities for each face. Common combinations:
- A/A: Both faces premium. Use for both-sides-visible parts like floating shelves and tabletops.
- A/B: Premium front, slightly less critical back. Good for cabinet doors that won't be seen from behind.
- A/C: Cabinet front, structural back. The most common cabinet-grade plywood, perfect when one face is finish-quality and the back is hidden inside a wall.
- B/C: Both faces decent but neither premium. Good for shop furniture and utility cabinets.
- C/D: Both faces rough. Sheathing, subfloor, blocking, anything structural.
Hardwood plywood vs softwood plywood
The grades above apply to both, but the lumber yard sorts them differently:
- Hardwood plywood (oak, birch, maple, walnut faces) is sold in graded thicknesses for furniture and cabinet work. Expect smooth, paint-or-stain-ready faces even at the lower grades, because the face veneer is selected for furniture use.
- Softwood plywood (Douglas fir, spruce, pine faces) is sold for construction. C and D grades are common; A and B are special-order. The faces are rougher even at the same letter grade.
When you see "Baltic birch" or "Russian birch" plywood at a hardwood specialty store, that's a separate grading system using BB/CC nomenclature. BB/BB Baltic birch is roughly equivalent to A/A hardwood plywood in surface quality - but Baltic birch has thinner, more numerous plies that give it superior strength and edge appearance.
Marine and exterior grades
Marine plywood uses an exterior glue that won't separate when wet, and the inner plies are also defect-free (no voids). This matters because a void inside the panel becomes a water trap, and marine plywood is rated for actual marine exposure. Don't pay for marine grade unless you need it - exterior CDX with proper sealing handles 90% of "outdoor" projects.
Which grade for which project?
| Project | Grade |
|---|---|
| Kitchen cabinet boxes (interior) | A/B or B/B hardwood |
| Cabinet doors (paint grade) | A/B hardwood |
| Cabinet doors (clear finish) | A/A hardwood, color-matched |
| Bookshelves and wall units | A/B hardwood |
| Floating shelves | A/A or A/B both faces visible |
| Garage shelving | C/D softwood, OSB also fine |
| Shop furniture | B/C or C/C softwood |
| Subfloor | C/D, T&G |
| Sheathing | C/D structural |
| Outdoor planter (built to last) | Marine or exterior A/C |
Saving money on grades
If you're paint-grading the project, drop one grade - paint hides minor defects. If you're staining, don't drop grades - stain shows everything.
For interior cabinet builds, buy A/A only for parts that show on both faces (floating shelves, free-standing dividers). Use A/C for everything else and orient the C face toward the wall, the floor, or the inside of a closed cabinet.
Need a cut list to plan around the panels you bought? Try the plywood cut calculator - set your stock material and the optimizer maps out parts to minimize the number of sheets you need.
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