Types of Plywood: Grades, Sizes and Uses

Plywood comes in two broad families. Construction (softwood) plywood — CDX, rated sheathing, tongue-and-groove subfloor, pressure-treated — is graded for strength and moisture resistance, and its job is to be covered by something else. Hardwood and appearance plywood — birch, maple, oak, Baltic birch, MDO — is graded by how the face looks, and its job is to be seen. Almost every bad plywood purchase comes from buying from the wrong family: cabinet birch on a shed roof, or CDX for a bookcase.

Within each family, three things decide the right sheet: the face grade (the letters), the exposure rating (how wet it can get), and for structural work the span rating (the two numbers on the stamp). Get those three right and the thickness mostly picks itself.

What Plywood Actually Is

Plywood is a stack of thin wood sheets called veneers or plies, peeled from a log on a lathe or sliced from it, then glued together under heat and pressure. The defining trick is cross-graining: each layer's grain runs at 90 degrees to the one beside it. Solid wood is strong along the grain and weak and unstable across it; alternating the direction cancels most of that out. The result is a panel that resists splitting at the edges when nailed, barely moves with humidity across its width, and is strong in both directions.

Panels are built with an odd number of layers — three, five, seven or more — so the grain on both faces runs the same way (lengthwise on a standard sheet) and the panel stays balanced rather than cupping. Sometimes two veneers are glued with their grain parallel to act as one thicker layer, which is why the industry distinguishes plies (individual veneers) from layers. A typical 1/2" sheathing panel has 3–5 plies; a 3/4" panel 5–7; 18 mm Baltic birch 13.

More plies of thinner veneer generally means a flatter, stiffer, more stable panel with fewer hidden gaps in the core, which is the single biggest quality difference between a cheap sheet and a good one of the same nominal thickness. The face veneer is only a small fraction of the total; what is inside decides whether a screw holds, whether the edge looks clean when cut, and whether the sheet stays flat on the rack.

Grain direction matters in use, too. A plywood sheet is noticeably stronger and stiffer along its length, parallel to the face grain — the strength axis. On a roof or floor, the long side always runs across the rafters or joists, never parallel with them.

Softwood vs. Hardwood Plywood

The names describe the face veneers and the grading system, not how hard the panel is.

Softwood plywood is made mostly from Douglas fir, southern yellow pine, spruce and other conifers, and in North America it is graded to the U.S. Voluntary Product Standard PS 1, usually through an agency such as APA. It is construction material: sheathing, subfloor, siding, concrete forms. Faces are rotary-peeled, which gives the wild, swirling grain most people picture when they think of plywood, and the grading is about knots, splits and patches rather than beauty.

Hardwood plywood has a thin face veneer of birch, maple, oak, cherry, walnut or similar over a core that may itself be hardwood veneer, softwood veneer, MDF or particleboard. It is graded under the ANSI/HPVA HP-1 standard, by appearance. This is what cabinets, built-ins, furniture and quality shelving are made from. It is not intended to be structural and generally carries no span rating, so it does not belong on a roof or floor no matter how thick it is.

Face Grades: A, B, C, D and CDX

Softwood plywood is labelled with two letters: the grade of the front veneer, then the back. An AC panel has an A face and a C back; CDX has a C face and D back. The veneer grades under PS 1 are:

Common Combinations

AC — one good, paintable face and a rough back. The panel for painted projects where only one side shows: outdoor signs, utility cabinets, a painted wall in a garage. Usually sold Exterior-rated.

BC — one solid face with some knots and plugs, and a rough back. A cheaper AC for shop furniture, shelving in utility spaces and anything painted where small blemishes do not matter. It is the "sanded pine" most big-box stores stock.

AB / BB — both faces sound. Used where both sides are seen, and in concrete-form panels.

CDX — C face, D back, exterior glue. The workhorse of residential framing for sheathing walls and roofs. It is unsanded, rough, and never meant to be looked at.

Many structural panels today skip the letters entirely and are sold simply as Rated Sheathing or Rated Sturd-I-Floor with a span rating — the performance number matters for that job, not the face appearance.

Exposure Ratings

The exposure durability classification on the stamp tells you how much water the bond line can take. It is the most important line on the stamp for any outdoor or wet-area project.

• Exterior — fully waterproof glue and C-grade or better veneers throughout. Designed for permanent exposure to weather or moisture: siding, soffits, outdoor projects, exposed shed walls. It still needs paint or sealer on the faces and edges to stop checking and weathering.
• Exposure 1 — the same waterproof glue but with D-grade veneers allowed. Built to survive normal construction delays and occasional wetting, then to be covered. This is nearly all sheathing and subfloor, including CDX and OSB.
• Interior — moisture-resistant rather than waterproof adhesive. Most hardwood plywood falls here. Fine indoors; it should not get wet repeatedly. Older references also mention "Exposure 2", a middle category that has been dropped from the current standards; you may still meet it on old stock.

"Exterior" does not mean rot-proof. An untreated exterior panel that sits wet against soil or in a puddle will decay like any untreated wood. Ground contact is a job for pressure-treated plywood with the right treatment level.

Span Ratings and the Grade Stamp

Every structural panel carries a stamp, usually on the back or edge. It lists the panel grade, the span rating, the thickness, the exposure classification, the mill number and the product standard (PS 1 for plywood, PS 2 for performance-rated panels such as OSB). If a structural panel has no stamp, an inspector can reject it.

The span rating on Rated Sheathing is two numbers separated by a slash, and it is the most useful thing on the stamp:

• The left number is the maximum spacing, in inches, of rafters or trusses when the panel is used as roof sheathing.
• The right number is the maximum spacing of joists when the panel is used as subfloor (under a separate underlayment or finish floor). A right-hand zero, as in 24/0, means the panel is not rated for floors at all.

So a 32/16 panel can sheathe a roof with supports up to 32" apart, or a floor with joists at 16". A 24/16 panel handles rafters at 24" and joists at 16". Both assume the strength axis runs across the supports, and roof ratings at the maximum spacing often assume the unsupported panel edges are held together with panel clips (H-clips) or tongue-and-groove edges. Local code, snow load and roofing weight can call for something heavier, so check the requirement before buying the minimum.

Single-floor panels — sold as Rated Sturd-I-Floor — carry one number instead of two: 16 oc, 20 oc, 24 oc or 48 oc, the maximum joist spacing when the panel serves as combined subfloor and underlayment. A 24 oc panel, normally 23/32" thick, is the default for houses on 16" or 19.2" joists.

Nominal vs. Actual Thickness

A sheet sold as "3/4 inch" is almost never 3/4 inch. Sanding at the mill and modern sizing standards leave most panels 1/32" thinner than the name — enough to matter when you cut a dado for a shelf, choose screws, or stack panels to match an adjoining floor.

Two practical consequences. First, measure the actual sheet with calipers before cutting joinery; a 3/4" router bit cuts a dado that leaves an 18 mm shelf rattling. Undersized plywood bits exist for exactly this reason. Second, imported hardwood plywood is often metric and labelled with the nearest fraction, so two "3/4" sheets from different suppliers can differ by a few hundredths of an inch.

Sheet Sizes

The standard sheet in North America is 4 × 8 feet (about 1220 × 2440 mm), sized to land on studs, joists and rafters at 16" and 24" centres. Other sizes you will see:

• 4 × 9 and 4 × 10 — wall sheathing for taller walls, so one sheet covers sill to top plate with fewer horizontal joints.
• 5 × 5 — the native size of Baltic birch. Some suppliers rip them or stock 4 × 8 versions at a higher price.
• 2 × 4, 2 × 2 and 4 × 4 project panels — cut-down sheets at home centres. Convenient in a hatchback, but the price per square foot is much higher than a full sheet.
• Tongue-and-groove floor panels — nominally 4 × 8 but with a net face width of about 47-1/2", because the tongue is not counted.

Most stores will make a few rough cuts on their panel saw for free or a small fee. Treat those cuts as transport cuts, not finished dimensions — they are rarely square to cabinet tolerances.

Treated, Marine, Baltic Birch and Overlays

Pressure-Treated Plywood

Pressure-treated plywood is softwood plywood forced full of a copper-based preservative — today usually copper azole, ACQ or micronized copper — to resist rot and insects. Look on the tag for the treatment's use category: UC3B for above-ground exterior use, UC4A for ground contact. A shed floor sitting on blocks a few inches from soil should be ground-contact rated, because the area underneath stays damp and has no airflow.

Two cautions. The copper corrodes plain steel, so use hot-dip galvanized or stainless fasteners and hardware rated for treated lumber. And treated plywood usually ships wet; it shrinks and can warp as it dries, so leave gaps and fasten it promptly. It also needs time before it will take a finish — see when you can stain pressure-treated wood.

Marine Plywood

Marine plywood is defined by what is inside: every ply is solid, with no core voids, bonded with waterproof glue. Panels built to the British BS 1088 standard use tropical hardwoods such as okoume or meranti; APA Marine panels use Douglas fir or western larch with A or B faces. The void-free core is what matters — on a boat, a single hidden gap is where water collects and rot begins.

It is not treated and not rot-proof. Its durability comes from the build quality plus the epoxy, paint or varnish you put over it. For a deck box, planter or kid's playhouse, exterior plywood with properly sealed edges does the job at a fraction of the price; marine plywood earns its premium on boats, docks and anything that will be soaked repeatedly.

Baltic Birch

Baltic birch is birch veneer all the way through — no softwood core — with many thin, void-free plies of equal thickness. That gives it stiff, flat panels, strong screw holding, and attractive striped edges that can be left exposed. It is the shop favourite for drawer boxes, jigs, shop furniture and modern-style furniture with visible edges. It is graded B (one-piece face), BB (colour-matched patches), CP and C, and usually sold in 5 × 5 sheets in metric thicknesses (6, 9, 12, 15, 18 mm). The face is less refined than a premium hardwood veneer, so cabinet makers often use it for boxes and something prettier for doors.

MDO and HDO

MDO (Medium Density Overlay) is exterior plywood with a resin-impregnated paper face fused on. It takes paint better than any wood face — no grain raise, no checking — which makes it the standard for outdoor signs, painted exterior trim, and painted cabinets and built-ins. HDO (High Density Overlay) has a harder, glossier resin face built for reusable concrete forms and abrasive uses; it is expensive and rarely needed at home. For one-off forms, Plyform (B-B, mill-oiled, form-rated plywood) or even CDX is enough.

Hardwood Plywood Grades

Hardwood plywood uses a different system: a letter for the face and a number for the back. Face grades run AA, A, B, C, D and E, from nearly flawless matched veneer down to faces with patches and colour variation. Back grades run 1 to 4: 1 is sound and smooth with no open defects, 4 allows open knots and splits that do not hurt strength.

• A-1 — premium face, sound back. For pieces where both sides show, such as cabinet doors or open shelving.
• A-2 / B-2 — good face, back with small repairs and colour variation. The common choice for cabinet boxes, where the back faces a wall or the inside.
• C-3, D-3 and "shop" grade — painted work, shop furniture and hidden parts.

The core matters as much as the face. Veneer core is lightest and holds screws best. MDF core is dead flat and ideal for painted doors and veneered panels but heavy and weak at edge screws. Combination core puts thin MDF layers under the face veneers over a veneer centre, giving a flat, smooth face with veneer-core strength — a good default for cabinets. How the face is cut also changes the look: rotary-cut is cheapest with a broad, wavy grain, while plain-sliced and quarter-sliced veneers look like solid boards.

All hardwood plywood sold in the US must meet federal formaldehyde emission limits (TSCA Title VI, aligned with California's CARB Phase 2). Panels labelled NAF (no added formaldehyde) use soy- or other non-formaldehyde adhesives if that matters for a nursery or tight house.

Plywood vs. OSB vs. MDF

OSB (oriented strand board) is made from large wood strands, aligned in layers and pressed with resin. A stamped OSB panel with a given span rating meets the same structural requirements as plywood with that rating, and it is now the majority of wall and roof sheathing in North American houses, mainly because it is usually cheaper.

Where plywood is worth the premium: subfloors in kitchens and bathrooms, anything under tile, roofs on a build that may sit uncovered through weather, and any project where the panel may get wet more than once. OSB's swollen edges telegraph through thin flooring and shingles. Premium resin-enhanced OSB subfloor panels narrow that gap considerably and are widely used in new construction.

MDF is not plywood at all — it is wood fibre and resin pressed into a uniform board. It has no grain, no voids and a perfectly smooth face, which makes it excellent for painted doors and trim. It is very heavy, sags under load, holds screws poorly at the edges, and is ruined by standing water. Keep it indoors and out of bathrooms unless it is a moisture-resistant grade.

Tongue-and-Groove Subfloor

Subfloor panels have a tongue on one long edge and a groove on the other. Locking the panels together makes the edges share the load between joists, so a heel or chair leg landing on a seam does not deflect one panel more than its neighbour. That is what prevents the squeaks and the hairline cracks that appear in tile and grout over square-edged sheets.

The usual specification for a house on 16" joists is 23/32" T&G, Rated Sturd-I-Floor 24 oc, plywood or OSB. On 24" joists step up to 7/8" or the 48 oc 1-1/8" panels. Installation basics that matter:

• Run the long dimension across the joists and stagger the end joints by at least one joist.
• Leave a 1/8" gap at panel ends and edges for expansion — the tongue-and-groove profile builds in the edge gap, but ends still need spacing.
• Glue every joist with subfloor construction adhesive, then fasten with ring-shank nails or screws, typically 6" apart at panel ends and 12" in the field. Glue plus fasteners stiffens the floor substantially and is the single best squeak prevention.
• Put the stamp side down if marked "this side down", and tap panels together with a block, never a hammer directly on the tongue.
• Locate joists before fastening a repair panel over an existing floor — a stud finder that reads through subfloor saves guessing.

Over the subfloor, finish floors have their own requirements. Floating vinyl and laminate need a flat, sound surface and sometimes a separate underlayment — see our guide to underlayment for vinyl plank. Nail-down hardwood generally wants at least 5/8" and preferably 3/4" plywood to hold cleats, which is covered in engineered vs. solid hardwood.

Which Plywood for Which Job

A Note on Tile

Tile fails over wood when the floor flexes. Most tile-industry installation methods for ceramic tile over wood joists call for a 3/4" T&G subfloor on joists at 16" with a stiff frame, plus cement backer board or an approved membrane. Natural stone is less tolerant still and typically calls for two layers of plywood under the backer or membrane. OSB and lauan are routinely excluded as a direct tile substrate. Follow the specific method your backer or membrane maker publishes, because the warranty depends on it.

A Note on Outdoor Projects

Plywood fails outdoors from the edges inward: end grain wicks water into the core and the plies separate. Prime and paint, or seal, every cut edge as well as both faces, and keep the bottom edge off the ground. For clear-finished outdoor plywood, a penetrating product from our exterior wood sealer guide works on the faces, while a bead of a quality exterior caulk closes the joints where panels meet trim.

Plywood Prices by Type

Panel prices are some of the most volatile in the building-supply business. OSB and sheathing plywood more than tripled during the 2021 spike and have swung widely since, and prices vary by region, retailer and season. Treat the figures below as typical 2026 ranges per full 4 × 8 sheet (5 × 5 for Baltic birch) at US retailers, useful for comparing types rather than budgeting to the dollar.

Two ways to save. Lumber yards and dedicated hardwood suppliers are often cheaper than home centres for hardwood and Baltic birch, and the quality is more consistent. And buying the right grade is usually cheaper than buying the "best" grade: an A-1 cabinet sheet for a garage shelf, or marine plywood for a planter, is money spent on qualities the job never uses.

Cutting and Storage Tips

Getting Clean Cuts

• Face up or face down? Splinters happen where the teeth exit. On a table saw the blade cuts downward, so put the good face up. With a circular saw or jigsaw the blade cuts upward, so put the good face down.
• Use a fine blade. A 40-tooth general blade is fine for sheathing; for veneered hardwood use a 60–80 tooth plywood or crosscut blade. Painter's tape along the line and a knife score through the face veneer reduce tear-out further.
• Support both sides of the cut. Lay the sheet on a sheet of rigid foam on the floor, or on 2×4s spanning sawhorses on both sides of the line, so the offcut neither drops nor pinches the blade. A straightedge clamped as a fence, or a track saw, gives cabinet-quality edges without a big table saw.
• Pre-drill near edges and for edge screws. Screws driven into plywood edges split the plies without a pilot hole, and hold far less well than screws into the face.
• Finish the edges. Iron-on veneer edge banding or a glued hardwood strip hides the plies on furniture-grade work. On painted plywood, fill edge voids and nail holes with wood filler or a quality spackle — the differences between fillers are covered in spackle vs. putty. For a clear finish on Baltic birch or maple, water-based polyurethane stays pale rather than ambering; a good brush for water-based poly makes a visible difference on large flat panels.

Storing Sheets So They Stay Flat

• Store flat on three or four evenly spaced supports (2×4 stickers), or on edge leaned only slightly against a wall with the bottom edge on a board, never directly on concrete.
• Let it acclimate. Bring hardwood plywood indoors for a few days before cutting cabinet parts, so it reaches the room's moisture content first.
• Cover outdoor stacks with a tarp that sheds rain but leaves the sides open to air. Wrapping sheathing tight traps moisture and grows mould.
• Seal or use it soon. Structural panels are designed to tolerate a few weeks of weather during construction, not a season. A roof left without underlayment for months is where Exposure 1 panels start to delaminate.

The Short Version

For structure, ignore appearance and buy by stamp: span rating that matches your joist or rafter spacing, Exposure 1 for anything that will be covered, and 23/32" T&G for floors. OSB is fine for walls and most roofs; plywood is worth the premium under tile and in wet rooms.

For outdoors, buy Exterior-rated, MDO or pressure-treated, and seal every edge. CDX is a construction-phase panel, not an outdoor one, and marine plywood is only worth it on the water.

For furniture and cabinets, buy hardwood plywood by face and core: A-2 or B-2 with a veneer or combination core for boxes, Baltic birch for drawers and exposed edges, MDO or MDF where everything will be painted.

And measure the sheet before cutting anything that has to fit. Nominal 3/4" is 23/32" — and that 1/32" is the most common reason a carefully cut dado ends up loose.

Frequently Asked Questions

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