Lumber grades tell you how many knots, splits and other characteristics a board is allowed to have, and therefore what it is fit for. Softwood and hardwood are graded in completely different ways. Softwood construction lumber is graded mainly for strength and use under the American Softwood Lumber Standard (PS 20), with a single set of names for framing lumber across the country. Hardwood is graded for how much clear wood a furniture maker can cut out of each board. This page explains both, how to read a grade stamp, and which grade to buy for common jobs. For actual sizes see the lumber dimensions chart.
Softwood framing lumber (dimension lumber) grades
Nominal 2 to 4 in thick softwood is produced as dimension lumber: stress graded and assigned design values under the National Grading Rule, which is part of the American Softwood Lumber Standard. The Wood Handbook notes that one set of grade names is used throughout the United States, while the design values for each grade vary by species. Grading is done visually by a trained grader or by machine.
| Grade | What it means | Typical use |
|---|---|---|
| Select Structural | Highest stress grade; fewest and smallest knots and the straightest grain | Where strength and stiffness matter most, or for exposed framing |
| No. 1 | High strength, good appearance; small, tight knots | Joists, rafters and headers where a higher design value is wanted |
| No. 2 | The general framing grade; larger knots allowed | Most joists, rafters, studs and plates; often sold as “No. 2 and Better” |
| No. 3 | Lower stress grade with large characteristics | Blocking, bracing and lightly loaded parts |
| Construction, Standard, Utility | Light-framing grades for 2x4s | General framing (Construction), lighter uses (Standard), blocking and bracing (Utility) |
| Stud | Graded for vertical use; straightness matters most | Wall studs, also offered in widths over 4 in |
Spans and allowable loads depend on species and grade together: a No. 2 Douglas-fir-larch joist does not span the same distance as a No. 2 spruce-pine-fir joist. Use the span tables your building department accepts and the grade and species printed on the stamp, not the grade name alone.
Boards and appearance (yard) lumber
The Standard divides yard lumber into two classes (PS 20, 6.3.1.1): Select, for natural and paint finishes, and Common, for general construction and utility. Select grades are named by letters such as B and Better, C Select and D Select, or by names such as Superior, Prime, Choice and Quality, depending on species and rule book; because they grade the better face, the back may be lower in quality. Common boards come in three to five grades such as No. 1, No. 2 and No. 3 Common, or Construction and Standard. The top common boards suit shelving, siding and paneling; the middle grades sheathing and subfloors; the lowest grades rough concrete forms. In cedar and redwood some grades are marked “heart” because the heartwood resists decay.
How to read a grade stamp
- Agency mark: the symbol of the grading agency accredited by the American Lumber Standard Committee (ALSC) that supervises the mill.
- Mill number or name.
- Species or species combination, for example SPF (spruce-pine-fir), Hem-Fir, DF-L (Douglas-fir-larch) or SYP (southern yellow pine). Combinations group woods with similar properties that are sold together.
- Grade, such as No. 2 or STUD.
- Moisture at surfacing: S-DRY (dry, 19% moisture content or less), KD (kiln dried to 19% or less) or S-GRN (surfaced green, over 19%). Some rules also allow marks such as KD-15 for lower limits.
- PS 20 section 2.8 requires the first five items on every grade mark. Treated lumber also carries a separate tag for the preservative and use category, and pallet or export lumber may be marked HT, heat treated.
Hardwood lumber grades
Hardwood lumber for furniture and cabinets is graded under the rules of the National Hardwood Lumber Association (NHLA) by cutting units: the share of a board that can be cut into clear pieces of at least a minimum size. The Wood Handbook summarises the main Factory grades as below. Except for F1F and Selects, the poorer face of the board decides the grade.
| Grade | Minimum clear-face yield (typical board) | Minimum width | Lengths | Good for |
|---|---|---|---|---|
| FAS (Firsts and Seconds) | 83-1/3% | 6 in | 8 to 16 ft | Long, wide clear parts: tabletops, doors, mouldings |
| F1F (FAS One Face) | FAS on the better face | 6 in | 8 to 16 ft | Like FAS where only one face shows |
| Selects | 91-2/3% on the better face | 4 in | 6 to 16 ft | Cabinet and furniture parts of moderate size |
| No. 1 Common | 66-2/3% | 3 in | 4 to 16 ft | Cabinet doors, face frames, shorter furniture parts; the best value for many shops |
| No. 2A Common | 50% | 3 in | 4 to 16 ft | Small parts, flooring, rustic work |
| No. 3A Common | 33-1/3% | 3 in | 4 to 16 ft | Small clear pieces and pallets |
| No. 3B Common | 25% sound (not clear) | 3 in | 4 to 16 ft | Utility and pallet stock |
For a hobby shop, No. 1 Common is often the best buy: it costs well below FAS, and two thirds of each board still comes out as clear parts, just in shorter pieces. Buy FAS when you need long, wide clear boards for tabletops or doors. Hardwood thickness is sold in quarters (4/4, 5/4, 8/4) and widths are random; the lumber dimensions chart lists rough and surfaced thicknesses, and the board foot calculator converts a pile of boards to board feet.
Common lumber abbreviations
| Abbreviation | Meaning |
|---|---|
| S4S | Surfaced four sides |
| S2S | Surfaced two sides |
| KD | Kiln dried |
| S-DRY | Surfaced dry (19% moisture content or less) |
| S-GRN | Surfaced green (over 19%) |
| HT | Heat treated (core held at 56 °C for 30 minutes) |
| R/L | Random lengths |
| FOHC | Free of heart center |
| VG / FG | Vertical (edge) grain / flat grain |
| T&G | Tongued and grooved |
| BTR | Better (as in No. 2 and BTR) |
| MBM | Thousand board feet |
Which grade to buy
- Wall studs: Stud grade or No. 2 SPF, Hem-Fir or SYP.
- Floor joists and rafters: No. 2 or better in the species your span table covers; No. 1 or Select Structural where a longer span is needed.
- Deck framing: No. 2 or better pressure-treated southern pine or the local treated species, with the treatment tag for ground contact where required.
- Shelving and painted trim: a top Common board grade, or Select for clear, knot-free boards.
- Furniture hardwood: No. 1 Common for most parts, FAS or Selects for long, wide clear pieces.
- Whatever the grade, pick individual boards: check for crook, bow, twist and cup, and look down the length of the board before buying.
Frequently asked questions
What is the best grade of lumber?
For softwood framing, Select Structural is the highest stress grade, followed by No. 1, No. 2 and No. 3. For hardwood, FAS (Firsts and Seconds) is the highest standard grade.
What does No. 2 lumber mean?
No. 2 is the general-purpose framing grade under the National Grading Rule. It allows larger knots than No. 1 and is what most joists, rafters and studs are made of; “No. 2 and Better” means the bundle may include No. 1 and Select Structural pieces.
What does KD on lumber mean?
Kiln dried. On a grade stamp, KD means the lumber was dried in a kiln to a maximum moisture content of 19% at the time of surfacing (PS 20, 6.2.6). S-DRY means dried to 19% by any method; S-GRN means surfaced green.
What is FAS lumber?
FAS (Firsts and Seconds) is the top NHLA hardwood grade: boards at least 6 in wide and 8 ft long that yield at least 83-1/3% clear-face cuttings (Wood Handbook Table 6-1).
What is a board foot?
PS 20 defines board measure as nominal thickness in inches times nominal width in feet times length in feet. A board foot is 144 cubic inches of nominal lumber, for example a 1 x 12 one foot long.
Sources
- USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (2010), chapter 6 (Commercial Lumber): hardwood Factory grades and Table 6-1, softwood yard and structural grades, retail grades.
- US Department of Commerce / NIST, Voluntary Product Standard PS 20-25, American Softwood Lumber Standard: sections 2.2, 2.7, 2.8, 2.12, 2.13, 6.2.6, 6.3.1.1 and Appendix C. Summarised in our own words.
- Certified grading rules of the ALSC-accredited agencies and the NHLA rules are the full grade descriptions; not reproduced.
Last reviewed: 24 October 2026. Related: lumber dimensions chart, lumber weight chart, plywood grades explained, board foot calculator. Spotted an error? Please let us know.