Two systems, not a hardness scale
Softwood and hardwood are botanical groups — conifers on one side, broad-leaved flowering trees on the other — and the Wood Handbook is plain that not all softwoods are soft nor all hardwoods hard. The distinction matters because each group is traded under its own rules: hardwood under the National Hardwood Lumber Association's rules, mostly for remanufacture into furniture, cabinets and millwork; softwood under the American Softwood Lumber Standard, mostly for construction. Hardness itself is on the Janka scale.
Hardwood grades
| Grade | Minimum width | Lengths | Clear-face cuttings, at least |
|---|---|---|---|
| FAS (Firsts and Seconds) | 6 in | 8–16 ft | 83-1/3% for most board sizes |
| F1F (FAS one face) | 6 in | 8–16 ft | As FAS on the better face |
| Selects | 4 in | 6–16 ft | As F1F on the better face; reverse not below No. 1 Common |
| No. 1 Common | 3 in | 4–16 ft | 66-2/3% for most board sizes |
| No. 2A and 2B Common | 3 in | 4–16 ft | 50% for most board sizes |
| No. 3A Common | 3 in | 4–16 ft | 33-1/3% |
From Wood Handbook Table 6–1, where the required share is higher for some board sizes and the number and minimum size of cuttings are set by board size; No. 3B Common and Sound Wormy are left out. Except for F1F and Selects, a board is graded from its poorer side. Not a complete statement of the NHLA rules.
The grade is about yield, not looks: it states the share of a board that can be cut into clear pieces of a minimum size. A board full of small knots between long clear stretches can still grade well; a board with a clear face but a defect that interrupts every cutting cannot. For short parts, a lower grade may supply all the clear pieces a project needs.
Softwood grades
- Select (appearance) lumber. For natural and paint finishes: trim, siding, flooring, paneling, finish boards. Grades by letters (B&BTR, C&BTR, C Select, D) or names (Superior, Prime, Choice) depending on species and rules; the reverse face may be lower in quality.
- Common boards. For construction and utility, in three to five grades by number (No. 1, No. 2) or name (Select Merchantable, Construction, Standard); knots grow larger and more frequent down the grades.
- Dimension lumber. Nominal 2 to 4 in thick, stress-graded under the National Grading Rule, with one set of grade names across the United States but allowable properties that vary with species.
- Factory and Shop. Softwood graded for cutting into parts, as hardwood Factory lumber is.
Note— Grades do not cross over
There is no single ladder from A to #1 across these systems. 'Selects' in hardwood and 'C Select' in softwood come from different rules, and plywood has its own grades again. Compare grades only within one rule book.
Rough and surfaced
| Term | What has been planed | Where you meet it |
|---|---|---|
| Rough | Nothing; sawn surfaces | Hardwood sold by the quarter, rough-sawn wood |
| S1S | One face; thickness by contract | Some hardwood orders |
| S2S | Both faces | Hardwood: 4/4 rough is 13/16 in S2S, 8/4 is 1-3/4 in |
| S4S | Both faces and both edges | Softwood dressed to size: 1 × 6 is 3/4 × 5-1/2 in, 2 × 4 is 1-1/2 × 3-1/2 in |
Hardwood thicknesses from Wood Handbook Table 6–4; softwood dry dressed sizes from PS 20 as tabulated by NIST. Every size is on the lumber dimensions chart.
Surfaced or 'finished' lumber is ready to cut but loses its rough thickness, and a board that was cupped or twisted when planed may already be thinner where it was flattened. Rough-sawn wood leaves the choice of final thickness to you — and the work of flattening it — and hides colour and some defects until it is planed. Board feet for hardwood are normally counted on the rough quarter thickness; the board foot calculator explains the convention.
Dry, kiln-dried and green
Under the American Softwood Lumber Standard, 'dry' lumber may hold up to 19% moisture; some grading rules mark KD 15 for 15% or less. Lumber for interior woodwork and furniture should be closer to 8% in most of the United States (6–10% for individual pieces), as the Wood Handbook recommends, which common softwood grades are not normally dried to. Green lumber, freshly sawn, holds far more water and will shrink as it dries. How much a board will move is worked out by the wood movement calculator, and its weight by the wood weight calculator.
Writing a lumber order
- Species, and whether hardwood or softwood rules apply
- Grade under the right rule book
- Thickness in quarters (hardwood) or nominal size (softwood)
- Rough, S2S or S4S
- Dry, kiln-dried or a moisture limit
- Quantity in board feet, linear feet or pieces, as the yard sells
Grain and figure are in wood grain; choosing and buying boards for a project in choosing lumber; and the quantity and cost of an order in the lumber calculator.
Sources
This is a summary: grading rules have many details, exceptions and species rules that are not repeated here, and the rule book of the grading agency governs. Sizes are the standards' own; a mill or yard may surface to other sizes by agreement.
- 1.
Chapter 6: Commercial Lumber, Round Timbers, and Ties. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Hardwood lumber in three categories (Factory lumber, dimension parts, finished products); NHLA grading from 1898 and by clear cuttings since 1932; the Factory grades FAS, F1F, Selects, No. 1 Common, No. 2A and 2B Common, No. 3A and 3B Common and Sound Wormy, with their minimum widths, lengths and clear-cutting yields (Table 6–1); inspection on the poorer side; random widths and 1-ft length steps; rough and S2S thicknesses (Table 6–4), S1S by contract; softwood yard lumber (Select and Common), structural lumber (dimension lumber under the National Grading Rule, timbers) and Factory and Shop lumber; grade names not interchangeable across species; the American Softwood Lumber Standard PS 20.
- 2.
Chapter 3: Structure and Function of Wood. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Softwoods and hardwoods defined botanically, not by hardness.
- 3.
Chapter 13: Drying and Control of Moisture Content and Dimensional Changes. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Dry softwood lumber as 19% moisture content or less under the American Softwood Lumber Standard; KD 15 as a 15% maximum in some grading rules; common softwood grades not normally dried to the values recommended for interior woodwork.
- 4.
NIST Handbook 130 (2026), IV.B Uniform Regulation for the Method of Sale of Commodities. National Institute of Standards and Technology, 2026.
Used for: Softwood nominal sizes and dry minimum dressed sizes under PS 20, including 1 × 6 at 3/4 × 5-1/2 in and 2 × 4 at 1-1/2 × 3-1/2 in.
About this guide
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