Plywood grades explained
Two systems are in use in the US. Construction plywood (sheathing, subfloor, “shop” sheets) is graded by veneer letters under NIST PS 1-22. Cabinet-grade hardwood plywood is graded by a face letter and a back number under ANSI/HPVA HP-1.
Construction plywood: N, A, B, C, D
Each face is graded on its own, and a panel is named face first: A-C is an A face with a C back. In brief, from the best:
From the standard, NIST PS 1-22, §5.4
- Grade N
- For a natural finish: all heartwood or all sapwood, no knots or open defects, at most two pieces across a 4 ft width, matched for color and grain, and only a few small wood repairs.
- Grade A
- Smooth and paintable: no knots, pitch pockets or open splits, and up to 18 neat repairs of wood or synthetic filler.
- Grade B
- Solid surface: sound, tight knots up to 1 in across the grain and repairs allowed, but no open defects; slightly rough grain is allowed.
- Grade C Plugged
- An improved C: openings no bigger than 1/4 × 1/2 in, sound tight knots up to 1-1/2 in, splits up to 1/8 in wide, and plugs and patches.
- Grade C
- Knotholes up to 1 in across the grain (an occasional one a little larger), tight knots and limited splits.
- Grade D
- Knots and knotholes up to 2-1/2 in across the grain, and any repairs that don’t seriously weaken the panel. The lowest grade.
The limits are for a 4 × 8 ft panel and scale for other sizes. Summaries in our own words; the standard has the full rules.
What CDX means
CDX is the trade name for C-D plywood sheathing with an Exposure 1 bond classification: a C face, a D back, and the X for Exposure 1, not “exterior”. PS 1 defines Exposure 1 as suitable for uses not permanently exposed to the weather: it is meant to survive getting wet during construction. Panels for long-term exposure are classed Exterior. APA says CDX panels should be used only where long-term weather exposure isn’t expected.
Only two sources publish this: APA and Wiss, Janney, Elstner
Hardwood plywood: AA to E, 1 to 4
The hardwood plywood standard is sold rather than published, so we give only what makers who print its grades agree on, and say who:
Hardwood plywood is graded face first, by letter (AA, A, B, C, D, E), then back, by number (1 to 4), written together as A-1 or C-3.
3 sources agree
AA is the top face grade; each letter after it allows more natural character and more repairs.
3 sources agree
D and E faces are meant for surfaces that won’t be seen, or will be painted.
Two sources: Columbia Forest Products and States Industries
Back grade 1 is the most restrictive; 2, 3 and 4 allow progressively more.
Two sources: States Industries and J. Gibson McIlvain
Thickness is on the plywood thickness chart, and Baltic birch has its own grade names: see Baltic birch plywood.
Sources
- NIST (US Department of Commerce) / APA, Voluntary Product Standard PS 1-22, Structural Plywood, §5.4, §5.10 and Table 10 (effective 2 October 2023), read 2026-11-07
- APA – The Engineered Wood Association, Plywood: selection criteria and bond classifications, read 2026-11-07
- Wiss, Janney, Elstner Associates, Exterior or Exposure 1 plywood: what’s the difference? (primer), read 2026-11-07
- Columbia Forest Products, The complete guide to choosing plywood (face grades AA–E, back grades 1–4), read 2026-11-07
- States Industries, Veneer options: face and back grades, read 2026-11-07
- J. Gibson McIlvain, Plywood grading confusion, read 2026-11-07