Lumber Grade Guide
What lumber grade stamps mean, and which grade fits which job.
Structural (framing) grades
Framing lumber is graded mainly on strength and appearance defects like knots, checks, and grain slope. From strongest/cleanest to most economical: Select Structural, No. 1, No. 2, and No. 3. Stud grade is a separate category specifically for vertical wall studs, allowing certain defects that wouldn't matter in that application. Most general framing in the US uses No. 2 or better -- it's the workhorse grade that balances strength and cost for typical residential construction.
Appearance grades
For trim, shelving, and visible work, appearance matters more than structural rating. Common grades include Select (premium, minimal defects) and Common grades (numbered 1-5, with increasing knots and defects). Choose based on whether the piece will be painted, stained, or seen up close.
Reading a grade stamp
A grade stamp typically shows the grading agency, mill number, species, grade, and moisture content (KD for kiln-dried, S-DRY for surfaced dry, S-GRN for green/unseasoned). Checking this stamp before buying tells you whether a board is suited to structural framing or better reserved for non-structural use.
Grade names and general definitions reflect standard US softwood lumber grading conventions used by grading agencies overseen by the American Lumber Standard Committee (ALSC). Always check your local building code for the minimum grade required for a specific structural application.
Frequently asked questions
What lumber grade should I use for framing?
No. 2 or better is the common default for general residential framing in the US -- it balances strength and cost for typical loads, though your local code or engineer may specify a higher grade for specific structural members.
What does "Stud grade" mean?
Stud grade is a specific category for vertical wall studs, allowing certain appearance defects that don't affect a stud's performance in that specific, non-bending application -- it's not a lesser grade, just a different-purpose one.
What does KD mean on a grade stamp?
KD means kiln-dried -- the lumber was dried in a kiln to a specified moisture content, as opposed to S-GRN (surfaced green/unseasoned), which still has higher moisture content and can shrink or warp more as it dries further.
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