Plywood Grades Explained: Choosing the Right Grade

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By Bikash Roy

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Bikash Roy

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· July 20, 2026

Standing in front of a plywood rack, the grade stamps alone can make choosing feel harder than it needs to be. This guide walks through matching a grade to a project before running quantities through the plywood calculator.

Step 1 — Decide Whether Appearance Matters

If the plywood will be hidden inside a wall, under flooring, or behind another finish material, appearance grade doesn’t matter — a utility grade like CDX (C-D veneer, Exposure 1 bond) is the standard, economical choice for subfloor, wall sheathing, and roof sheathing. If a face will be visible in the finished project (a cabinet side, a shelf, furniture), an A- or B-faced panel is worth the added cost.

Step 2 — Match Exposure Rating to Actual Moisture Exposure

Use Exterior-rated plywood for anything that will face permanent outdoor exposure (a shed exterior, an outdoor structure with no other weather barrier). Use Exposure 1 for structural applications that might see temporary moisture during construction but will ultimately be protected — this covers most subfloor and wall sheathing under a normal building envelope. Don’t default to Exterior “just to be safe” for interior structural work — it typically costs more without adding a benefit once the building is weathertight, and don’t substitute Exposure 1 for genuinely permanent outdoor exposure, since it isn’t rated for that.

Step 3 — For Structural Work, Check the Span Rating Against Your Framing

Any panel used as sheathing or subfloor should carry a span rating matching (or exceeding) the actual on-center spacing of the joists, rafters, or studs it will span. A panel rated for 16-inch floor spacing shouldn’t be used over 24-inch-on-center framing, regardless of how thick it feels by hand — thickness alone doesn’t guarantee adequate span rating, since internal ply construction affects stiffness too. See the plywood grading & span rating terms glossary for how to read the span rating numbers on a stamp.

Step 4 — Pick Sanded vs. Unsanded Based on the Finished Surface

Sanded plywood (A-C, B-C, and similar grades with at least one sanded face) is meant for surfaces that will be seen, painted, or finished. Unsanded sheathing-grade plywood is rougher and cheaper, appropriate anywhere the surface will be covered or isn’t cosmetically relevant — using sanded plywood for hidden subfloor is paying for a finish quality that will never be seen.

Step 5 — Consider Specialty Grades for Specific Needs

• Marine-grade plywood uses a higher standard of void-free core construction and durable adhesive, intended for boat-building and constant-moisture applications — considerably more expensive than standard exterior-rated plywood, and usually overkill for typical outdoor construction that just needs weather resistance rather than near-constant water contact.
• STURD-I-FLOOR panels are engineered to serve as combined subfloor-and-underlayment in one panel, potentially saving a separate underlayment layer — worth checking if a project’s design allows for single-layer flooring construction.
• Underlayment-specific panels are thinner panels meant to go over an existing subfloor before finish flooring, not to replace structural subfloor on their own.

Common Grade Choices by Project

Bottom Line

Match veneer grade to whether the surface will be seen, exposure rating to actual moisture conditions, and span rating to the real framing spacing — then use the plywood calculator to figure out how many sheets of the correctly chosen grade to buy. See common plywood calculation mistakes for what happens when grade and span rating get mismatched to the actual job.