A lumber grade ranks each piece of wood by the natural characteristics and manufacturing imperfections that affect its strength and its best use, under grading rules that conform to the American Softwood Lumber Standard, PS 20. For softwood dimension lumber, the grades you will see on most stamps are Select Structural, No. 1, No. 2, No. 3, Stud, Construction, Standard, and Utility, and the grade, species, mill, and moisture condition are all printed right on the piece.
As the Western Wood Products Association puts it, dimension lumber grading rules "limit natural characteristics and manufacturing imperfections," and the grades "are based on a visual or digital scan evaluation of each lumber piece." A higher grade allows fewer of those characteristics and carries higher design values, and a lower grade allows more of them and belongs in work where strength or looks matter less. Everything else, the stamps, the species marks, and the moisture codes, is the paperwork that proves which grade a piece earned.
Who writes the grading rules
Grades are not set by each mill on its own. Rules-writing agencies publish the rules and supervise the mills that grade under them.
- WWPA (Western Wood Products Association) writes the rules for western species. Its rules "establish standards of size and levels of quality in conformance with" PS 20, and WWPA is certified by the American Lumber Standard Committee as a rules writing and inspection agency, per its page on interpreting grade stamps.
- SPIB (Southern Pine Inspection Bureau) writes the rules for Southern Pine, and the Southern Pine grade descriptions quoted below are based on SPIB grading rules.
- NLGA (National Lumber Grades Authority) publishes the Standard Grading Rules for Canadian Lumber. The current edition is the 2025 edition, dated September 2025, with Supplements No. 1 and No. 2 effective May 1, 2026.
The Canadian rules also draw size lines worth knowing at the counter. As summarized by the Canadian Lumber Standards Accreditation Board, boards are less than 2 inches thick (nominal), lumber runs from 2 to 5 inches, and timber is anything greater than 5 inches.
The dimension lumber grades, top to bottom
Dimension lumber, the 2x4s through 2x12s that make up most of what moves through a yard, runs from Select Structural at the top down through Utility. Here is how the Southern Pine grade descriptions, based on SPIB rules, describe each grade for dimension lumber 2 to 4 inches thick.
| Grade | What the description says | Recommended use |
|---|---|---|
| Select Structural | High quality, limited in characteristics that affect strength or stiffness | Where high strength, stiffness, and good appearance are desired |
| No. 1 | Recommended where strength, stiffness, and appearance all matter | Construction where high strength, stiffness, and good appearance are desired |
| No. 2 | Allows well-spaced knots of any quality | Most general construction uses where moderately high design values are required |
| No. 3 | Many pieces would qualify as No. 2 except for a single limiting characteristic | General construction where appearance is not a controlling factor |
| Stud | Composite of No. 3 strength and No. 1 nailing edge characteristics | Stud uses, including load-bearing walls |
| Construction | Good appearance, graded primarily for strength and serviceability (2 to 4 inches wide only) | General framing |
| Standard | Characteristics limited for good strength and serviceability (2 to 4 inches wide only) | Same purposes as Construction |
| Utility | 2 to 4 inches wide only | Where economical construction and good strength are wanted together |
WWPA sorts western species into size categories, and the category decides which grade names apply:
- Structural Light Framing, 2x2 through 4x4, for "high-strength design values" in light framing sizes "such as in engineered wood trusses": Select Structural, No. 1 & BTR (Douglas Fir-Larch, Douglas Fir, and Hem-Fir only), No. 1, No. 2, and No. 3.
- Light Framing, 2x2 through 4x4, the "basic framing lumber" for wall framing, sills, plates, cripples, and blocking: Construction, Standard, and Utility.
- Stud, 2x2 through 4x18, "an optional grade intended for vertical use, as in load bearing walls."
- Structural Joists & Planks, 2x5 through 4x18, for floor and ceiling joists, rafters, headers, small beams, trusses, and general framing: Select Structural, No. 1 & BTR, No. 1, No. 2, and No. 3.
How to read a grade stamp
The stamp is the piece's report card, and it is not graded on a curve. WWPA says most of its grade stamps, other than those on rough lumber and heavy timbers, carry five elements:
- Certification mark, showing the piece was graded under the agency's supervision.
- Mill identification, either an assigned mill number or the firm's name or brand.
- Grade designation, such as No. 2 or Stud.
- Species, as an individual or combined species name.
- Seasoning, the moisture condition at the time the piece was manufactured.
The seasoning mark is the one that trips people up, so here is the decoder from WWPA's stamp guide.
| Mark | Meaning |
|---|---|
| MC-15 or KD-15 | 15% maximum moisture content |
| S-DRY or KD | 19% maximum moisture content |
| S-GRN | Over 19% moisture content (unseasoned) |
Two pieces can share a grade and differ on the seasoning mark, so when a job calls for dry material, read the whole stamp before the load goes out.
Dense and non-dense Southern Pine
Southern Pine adds one wrinkle: several of its grades come in dense and non-dense versions, so the same yard can stock No. 2 Dense alongside No. 2 Non-Dense. When the plans want Dense, they say so by name. You do not need to memorize the definition to sell it correctly, but you do need to stock it as its own item, mark the rack, and hand over what the plans ask for.
Appearance grades and boards
Not everything in the shed is graded for structure. The Southern Pine descriptions cover the common appearance and board grades:
- C&Btr combines the B&B and C grades and "satisfies requirements for high-quality finish."
- D is an "economical, serviceable grade for natural or painted finish."
- No. 2 boards are for "good-quality sheathing, fencing, shelving and other general purpose uses," and design values are not assigned to them.
Hardwood plays by a different set of rules
If your yard stocks oak, poplar, or maple for cabinet shops and trim carpenters, leave the softwood table at the door. Hardwood lumber is graded under National Hardwood Lumber Association (NHLA) rules, and the logic is different: the grader measures how much clear wood a board will yield once it is cut into parts. As the American Hardwood Export Council summarizes the rules, the grades run FAS, FAS One Face (F1F), Selects, No. 1 Common, No. 2A Common, and No. 2B Common, with No. 2 Common combining 2A and 2B, and a board's grade comes down to its poorer face.
The two you will hear most often:
- FAS needs a board 6 inches and wider and 8 feet and longer, yielding 83-1/3% (10/12ths) to 100% clear-wood cuttings, and both faces must meet the FAS minimum.
- No. 1 Common needs a board at least 3 inches wide and 4 feet long, yielding from 66-2/3% (8/12ths) up to the FAS minimum.
Hardwood thickness is named in quarters, so 4/4 is one inch and 8/4 is two inches, and our board foot calculator walks through how hardwood board feet are tallied.
What grades mean for your yard
Here is where the grading rules stop being trivia and start being margin. Every grade of the same size is a separate item in your system, with its own cost from your vendor and its own price at the counter. A 2x4x8 Stud and a 2x4x8 No. 2 are different SKUs, and if your inventory lumps them together, the counts will be wrong on both and your cost of goods will drift every time a truck lands. Our guide to SKUs vs UPCs covers the item setup side.
A few habits keep grades straight from the truck to the ticket:
- Put the grade and species in the item description, so the person ringing up a contractor sees "2x4x8 SPF STUD" and not a bare "2x4x8" that could be anything.
- Tag the rack with grade and species, because the Saturday crew will sell what they can find, and a No. 2 that goes out at the Select Structural price is a gift nobody asked for, while the reverse is money you donated.
- Receive by grade and species against the purchase order, so a substitution from the vendor gets caught at the dock instead of at month end.
- Count by grade, so a cycle count that finds 1,200 pieces of 2x4x8 also tells you how many are Stud and how many are No. 2 before you write the next order.
The other habit is knowing where the yard's job ends. Which grade a wall or a header needs is decided by the contractor's plans, the engineer, or the building inspector, and the yard sells what the stamp says and what the plans call for. When a customer asks whether No. 3 will carry their deck roof, the right answer is that the plans or the inspector make that call.
For the money side, the guide to lumber pricing covers pricing per MBF, per piece, and per lineal foot, and the guide to material takeoffs covers turning a set of plans into a quote. The lumber yard POS and inventory guide lays out what your software needs to handle along the way.
How Rundoo handles graded lumber
In Rundoo, you set each grade up as its own product, and units of measure come from one company list (EA, PC, LF, BF, MBF, unit, pallet) with per-product conversions, so a No. 2 2x4 can be priced per MBF and sold by the piece without anyone doing board foot math at the register. Inventory shows on hand, committed, available, and on order from the sale, and your crew can receive by scan and cycle count on the phone out in the yard, one grade at a time. More on how it fits a yard is on our lumber and building materials page.
