Interpreting Grade Stamps

img07tnWestern Wood Products Association is one of the largest associations of lumber manufacturers in the United States, representing sawmills in the 12 western states and Alaska. The Association's Quality Assurance Division supervises lumber grading by maintaining a highly competent staff of lumber inspectors who regularly check the quality of mill production, including visual grade requirements of glued products and machine stress-rated lumber.

The Association's Grading Rules for Western Lumber establishes standards of size and levels of quality in conformance with the American Softwood Lumber Standard PS 20. WWPA is certified as a rules writing and inspection agency by the Board of Review, American Lumber Standard Committee and is approved to provide mill supervisory services under its rules and the rules of the West Coast Lumber Inspection Bureau, the Redwood Inspection Service, the National Lumber Grades Authority for Canadian Lumber and the NGR portion of the Southern Pine Inspection Bureau Rules. In addition, WWPA is approved to supervise finger-jointed and machine stress-rated (MSR) lumber.

Interpreting Grade Marks

WWPA uses a set of marks to identify lumber graded under its supervision. The grade marks are stamped on the lumber and appear near the ends of the product:


Most grade stamps, except those for rough lumber or heavy timbers, contain 5 basic elements:

WWPA certification mark - This symbol indicates that lumber bearing this trademark has been graded under the supervision of Western Wood Products Association.

Mill identification - The originating mill is identified by an assigned mill number or by the firm's name or brand. The WWPA Mill Number List may be accessed here.

Grade designation - The grade is shown by the grade name, number or abbreviation.

Species - indicates species by individual or combination species name.

Seasoning - The moisture content or conditioning of the piece at the time of manufacturing:

MC-15, KD-15

15% maximum moisture content


19% maximum moisture content


over 19% moisture content (unseasoned)

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