Plywood Grade Stamps Explained: What AC, BC, CDX, and B-2 Allow — Plus July 2026 Prices
Plywood Grade Stamps Explained: What AC, BC, CDX, and B-2 Allow — Plus July 2026 Prices - A step into the workshop.
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We've all been there: standing in the plywood aisle with a flatbed cart, phone in one hand, twenty minutes before school pickup, staring at a stamp that reads C-D EXPOSURE 1 32/16 and trying to remember whether that's the good one. Every sheet looks the same on edge. The prices absolutely do not. And somewhere in your memory is the last bargain sheet, the one with the hidden hole that collapsed under a screw and the knot that ghosted up through two coats of paint.
Those stamps aren't marketing. I've pulled the actual defect allowances from the standards and paired them with real shelf prices from this month, so you can decide at the rack instead of regretting it at the router table.
Two Rulebooks Are Sharing One Rack
The first thing to sort out is that two separate grading systems live side by side at the lumberyard, and they don't speak the same language.
Construction plywood, the pine and fir stamped AC, BC, or CDX, is graded under Voluntary Product Standard PS 1-19, published by NIST, with APA – The Engineered Wood Association doing most of the certifying. Its code is two letters: face veneer grade first, back grade second.
The hardwood "cabinet" panels, your maple and birch, follow ANSI/HPVA HP-1-2024 from the Decorative Hardwoods Association. That system uses a letter for the face (AA at the top, down through A, B, C, D, and E) and a number for the back (1 through 4). So B-2 is not a typo for BB. It's a B face over a number-2 back, from a different standard entirely, and a B in one system is not a B in the other.
What the Letters Actually Allow
PS 1-19 spells out, defect by defect, what each softwood veneer grade can contain on a 4x8 sheet:
- A must be free of knots and open defects, but it may carry up to 18 repairs, and a single wood patch can run 2-1/4 by 4-1/2 inches. A means paintable, not perfect.
- B is a solid surface allowing sound, tight knots up to 1 inch and splits no wider than 1/32 inch.
- C permits open knotholes up to 1 inch in any number, plus tight knots to 1-1/2 inches.
- D permits knotholes to 2-1/2 inches, with an occasional 3-incher.
Read that list again and the pattern jumps out: every step down the alphabet roughly doubles the size of hole the standard tolerates. That one sentence is the whole system. It's also why D veneer hiding one ply below the surface is exactly what dips and telegraphs through paint on cheap sheathing.
The CDX Trap: That X Isn't What You Think
Under PS 1-19, the panel the trade calls CDX is a C face over a D back and D inner plies, unsanded, with an Exposure 1 bond. The X refers to exterior-type glue. It does not make the sheet an Exterior panel, and APA's own product guide says so bluntly: all-veneer rated sheathing Exposure 1, "commonly called 'CDX' in the trade, is frequently mistaken as an Exterior panel and erroneously used in applications for which it does not possess the required resistance to weather." PS 1-19 is just as clear that bond classification covers the adhesive's moisture resistance, not the panel's resistance to erosion, UV, mold, or decay. The glue in CDX will survive the rain; the D veneer around it won't.
A-C and B-C are the genuine Exterior panels: sanded both sides, C inner plies, and the Exterior grade table in PS 1-19 permits no D veneer anywhere in the sheet. For something permanently out in the weather where neither side shows, APA's answer is C-C Exterior. While you're reading stamps, that fraction like 32/16 on sheathing is the span rating: maximum roof-support spacing in inches on the left, subfloor spacing on the right.
B-2, Translated for the Cabinet Aisle
Over in the hardwood racks the faces get fussier, because these are the panels you'll finish clear. Under HP-1-2024, a B face on maple or birch allows around eight conspicuous pin knots per 4x8 panel and roughly four scattered sound knots no bigger than 3/8 inch. Columbia Forest Products, whose PureBond panels (the hardwood ply you'll find at the big boxes) are built to this standard, calls B "cabinet grade," sends C faces to cabinet interiors and shelves, and saves D and E for parts that stay hidden or get painted. The number is the back: a grade-2 back may carry up to sixteen sound, tight knots as large as 3/4 inch plus repaired knotholes to 1/2 inch, all still adding up to a sound surface. A B-2 panel is built to show one good side, so plan your cut list around that.
Two more things hide under the veneer. Inner plies carry their own grades, J through M: J allows no knotholes at all, M permits openings up to 2-1/2 inches, and on interior-glue panels with a C face or lower, plies allowing 1-inch openings can sit directly beneath the face. And the face itself is thinner than you'd guess: HP-1-2024 describes decorative face veneers as generally 1/38 inch (0.026 inch) and thinner, and notes that panel hardness depends more on what's underneath than on the maple you can see. A maple face does not make a maple-hard panel.
Two quick asides. Every HP-1 panel has to meet the 0.05 ppm CARB/EPA formaldehyde limit, which is reassuring when the bookcase is headed for a kid's room. And none of this is Baltic birch, which has its own supply saga we covered in an earlier piece; the birch prices below are domestic-market hardwood ply.
What Your Tape Measure Will Really Find
"3/4 inch" is a label, not a measurement. The industry designation for 3/4 nominal construction plywood is the 23/32 Performance Category, and PS 1-19's Table 10 gives you numbers you can check with calipers: a sanded 23/32 panel must measure between 0.703 and 0.734 inch. (A sanded panel actually stamped 3/4 Performance Category must run 0.734 to 0.766.) Hardwood plywood is looser still: HP-1-2024 says thickness classes are not to be expressed as actual measurements, and a 3/4 Class panel only has to reach the stated size minus 3/64 inch, a floor of 0.703, and that's checked before the final sanding.
Then there's the metric wrinkle. Much hardwood and import plywood is really an 18 mm product, which converts to 0.709 inch, sold right beside the inch-labeled sheets; McCoy's stocks an 18 mm paint-grade birch on the very same rack, and TT Plywood cautions that although 18 mm and 3/4 inch get treated as equivalents, they are not always interchangeable.
The practical upshot: cut a dado with a true 3/4-inch bit and every sheet in that 0.703-to-0.734 band rattles in it, with up to 3/64 inch of slop. Measure the sheet you actually brought home and cut the joint to fit. Of everything in this article, that habit has saved me the most re-cut shelves.
What a Sheet Costs This Month
Here's McCoy's Building Supply's rack as of July 28, 2026, all 4x8 sheets:
| Panel | Thickness | Price |
|---|---|---|
| CDX sheathing, 3-ply | 15/32 | $25.99 |
| CD sheathing | 23/32 | $39.49 |
| BC sanded | 23/32 | $52.49 |
| Birch C-2 | 1/2 in. | $53.99 |
| Birch paint-grade | 18 mm | $57.99 |
| Birch D-3 | 3/4 in. | $85.99 |
The aisle math worth memorizing: same store, same 23/32 thickness, the B face costs $13.00 over CD sheathing, roughly a 33 percent premium. (McCoy's stocks AC only in 1/4 inch, at $29.19, so I can't give you a verified 3/4 AC price.)
For a second data point, the GlassIt price tracker had Lowe's Plytanium 23/32 pine rated sheathing at $38.88 on July 14, 2026, inside a recorded range of $30.85 to $42.90. Woodworking Advisor's July roundup of Lowe's lists 23/32 Douglas-fir CDX at $39.00, 3/4 sanded plywood at $69.85 to $74.98, and 1/2 maple at $61.38. Home Depot numbers only reach me through third-party roundups, so treat them as ballparks rather than shelf tags: Home Improvement Way anchors the aisle at roughly $15 for OSB, $28 for BCX, and $55 and up for birch, while Woodworking Advisor's range table puts 3/4 utility pine at $35 to $55 and 3/4 birch at $55 to $80.
Matching the Sheet to the Job
So when is the cheap sheet fine? My honest read of the standards and the shelf tags:
- Garage shelves, jigs, and shop fixtures nobody inspects: CD at $39.49 is plenty. Just remember it comes unsanded.
- Anything painted where the surface matters: that $13 jump to BC is the cheapest upgrade in the aisle. A B face is a solid surface with knots tight and capped at 1 inch, and BC is a true Exterior panel besides.
- Anything living outside permanently: C-C Exterior for hidden work, A-C where one side shows. Not CDX, no matter how friendly the price.
- Clear-finished built-ins and furniture: hardwood B-2 for the show faces, C faces inside the boxes, following Columbia's own guidance.
Whatever you buy, do the five-minute version of what this article does. Read the stamp before the price tag, and put calipers on the sheet before you cut a single joint. The stamp tells you what the mill was allowed to hide; the calipers tell you what they actually sold you.