Two sheets of plywood can look identical and differ by $40 a panel. The grade letter is what separates them.
Quick answer: Plywood grades run from A to D, with A the highest quality and D the lowest. Softwood plywood uses two letters (face + back), so AB means an A-grade face and a B-grade back. Use A or B grades for visible surfaces, and C or D grades for structural work that will be hidden, painted, or covered.
Here is how the grading system works, which grades fit common projects, and what to check before you buy.
Plywood Grades at a Glance
| Grade | What you get | Best used for |
| A | Smooth, defect-free, paint-ready surface (highest cost) | Cabinet faces, furniture, visible panels |
| B | Minor flaws, repairable knots, slightly less smooth | Painted surfaces, semi-visible areas |
| C | Visible knots up to 1.5 inches | Subfloors, sheathing, hidden structure |
| D | Large flaws and knots up to 2.5 inches (lowest cost) | Temporary structures, underlayment, throwaway formwork |
Hardwood plywood adds a back-number system: 1 is the best back, 4 is the worst. So A1 is premium and D4 is the most economical.
What Do Softwood A, B, C, and D Grades Mean?
Softwood plywood is graded on both sides. The first letter is the face veneer and the second is the back. An “AB” panel has an A-grade face and a B-grade back. This system is defined under the U.S. PS 1-09 standard, so grades are consistent across brands.
- A-grade: Sanded smooth, no open defects. Worth the premium when the surface will be seen, and it takes paint evenly.
- B-grade: Small natural flaws or repaired knots. Fine for painted panels and utility surfaces.
- C-grade: Sound but visually flawed, with knotholes up to 1.5 inches filled or open. Structural, not decorative.
- D-grade: Unrepaired knots up to 2.5 inches. Choose it when cost beats appearance, for formwork, underlayment, or covered sheathing.
How Hardwood Plywood Grades Differ from Softwood
Hardwood plywood (birch, maple, oak, and others) grades faces with the same A-to-D letters but backs with numbers, 1 (best) through 4 (sound but utilitarian). An A1 panel is the premium choice for furniture and cabinetry; A2, B1, and B2 fit most visible work; and D4 is the economical option for hidden parts.
Common Two-Letter Codes You Will See
- AB, AC, BC: Face quality stepping down, back still serviceable. Common in cabinet and furniture stock.
- CDX: C face, D back, and the X means the glue can handle limited moisture exposure. A standard for roof sheathing and garage construction.
- Sanded Pine / Sandeply: BC-level sanded panels with a smooth surface that holds fasteners well. Popular for shop cabinetry and indoor projects.
Which Grade Do You Need?
- Both sides visible: A1, A2, B1, or B2.
- Only one side shows: A4 or B4 saves money without sacrificing the visible face.
- Clear finish (stain or natural): stick with A1 or A2.
- Painted finish: B grade or lower on faces, 3 or lower on backs.
- Outdoor use: look for exterior-rated panels (the X in CDX) and consider pressure-treated or marine grade plywood for long-term wet exposure like boat hulls and cisterns.
Grading sets a floor for quality, not a ceiling. Still inspect sheets in person for grain pattern, flatness, and edge condition before committing to a project list. If the use case is unclear, match the grade to the finish: visible and clear means A, painted means B, hidden means C or D. For a deeper look at choosing panels by project type, see our guide on how to choose the right plywood for cabinets.
Frequently Asked Questions
What is the highest grade of plywood?
A1. That is an A-grade face with a closed 1 back in hardwood terms, which is the premium panel for furniture and casework.
Is CDX good for outdoor projects?
Only for covered applications like roof sheathing or sheathed sheds. The X glue rating tolerates incidental moisture, not long-term weather exposure. Use pressure-treated or marine grade instead.
Does grade affect strength or just appearance?
Primarily appearance. C and D panels are structurally sound, but open flaws weaken surface consistency and finishing. For load-bearing work, species and thickness matter more than letter grade.
What is the cheapest plywood grade?
D grade (or D4 in hardwood). Ideal for throwaway formwork, temporary covers, and underlayment that gets sealed or hidden.
Find the Right Plywood Grade at Forest Plywood
We stock everything from A1 hardwood panels to CDX sheathing at both La Mirada and National City. If you are not sure which grade fits your project, our team will help you spec it before you order. Call us at 800.936.7378 or visit either location.
