What Is Lumber Grade (Standards Chart)
Lumber grade is a classification assigned under a set of grading rules. It describes permitted characteristics, such as knots and splits, but is not a universal strength rating. Use the chart below to understand common U.S. softwood grades, then check the piece’s species, grade stamp, moisture designation, project plans, and applicable code before choosing lumber for structural work.
What lumber grade means
A lumber grade identifies how a piece measures up to rules for its species or species group. Those rules limit or allow features that affect strength or appearance. A grade helps buyers and builders sort lumber, but its name alone cannot show whether a board is suitable for a particular span, load, or project.
For structural softwood lumber, trained graders or approved grading processes assess characteristics under rules set by a recognized grading agency. The stamp ties the lumber to a grade and other information, such as species or species group. The applicable rules depend on the lumber and the grading system.
One key point: grade is not the same as a complete engineering rating. Design values depend on factors including species or species combination, grade, member size, loading direction, and design conditions. A general chart can explain grade names, but it cannot tell you whether a joist or beam is large enough for a specific job.
In my equipment and building-materials instruction, I’ve found that people often read “No. 2” as a complete strength specification. It is only one part of the description. Think of the grade as a label that must be read with the species and project requirements.
Common U.S. softwood lumber grades: standards chart
This chart gives a broad orientation to common U.S. softwood grades. It is not a universal strength ranking, and grade names do not mean exactly the same thing across every species, product, or grading rule. Match the grade to the project documents and applicable design values.
| Grade or designation | General meaning | Typical use guidance |
|---|---|---|
| Select Structural | A high structural stress grade in the common dimension-lumber sequence. | Higher-demand structural uses only when design values and project documents permit. |
| No. 1 | Generally allows fewer or less severe characteristics than No. 2 under the applicable rules. | Structural framing when the specified species and grade meet the design. |
| No. 2 | A common structural framing grade. It allows more or larger characteristics than higher grades under the applicable rules. | General framing when plans and code allow it. |
| No. 3 | Allows more characteristics than No. 2 under the relevant grading rules. | Limited or lower-demand uses only when the project permits it. Do not treat it as a direct substitute for No. 2. |
| Stud | A grade intended for stud use, with its own grading provisions. | Stud applications when the design and code accept the grade. |
| Construction, Standard, Utility | Other grade names used under applicable grading rules. | Use only where the governing rules and project requirements allow them. |
The chart does not compare lumber across all species. For example, No. 2 from one species group is not automatically equivalent to No. 2 from another. The grade name alone does not supply a safe span or load limit.
For U.S. softwood lumber, relevant references include the current American Softwood Lumber Standard, DOC PS 20, the rules of the applicable grading agency, and the National Design Specification (NDS) Supplement for design values. A builder or designer should use the current versions that apply to the project.
How to read a lumber grade stamp
A grade stamp is the piece’s identification mark. It commonly shows a grading agency, mill identification, species or species combination, grade, and a moisture or seasoning designation, when applicable. Read the full stamp rather than relying on one large grade label.
Stamp layouts differ. Check each part against the project specification, and ask the supplier or grading agency about a mark you cannot identify. A stamp does not, by itself, certify the member’s actual dimensions, span, installation, or adequacy for a particular load.
Moisture terms are useful when comparing lumber or planning for movement:
- S-GRN means surfaced green lumber, generally above 19% moisture content.
- S-DRY means surfaced dry lumber, generally at 19% moisture content or less at surfacing.
- KD-19 and KD-15 indicate kiln-dried lumber to the respective maximum moisture-content limits under the applicable grading rules.
The 19% figure is a designation boundary used in these terms, not a promise that every piece will remain at that moisture level after delivery. Wood can gain or lose moisture as its surroundings change. Follow the project requirements for moisture condition and allow for movement where needed.
If the stamp is missing, unreadable, or does not match the plans, do not guess based on the board’s appearance. Ask the supplier for documentation or seek verification from an authorized grading agency.
Choosing lumber for structural or appearance use
Structural grade and appearance grade answer different questions. Structural grading concerns characteristics that affect use under load. Appearance grading focuses on visual features. A board that looks smooth or attractive is not automatically suitable for a structural member.
For a structural project, use the plans and code to confirm the required species or species group, grade, size, moisture condition, and treatment. Design values must match those details. A general chart cannot size a beam, joist, or column; use the project’s design documents or consult a qualified building professional when a requirement is unclear.
Hardwood appearance grades, including grades from the National Hardwood Lumber Association (NHLA) system, use a different grading approach. They do not directly establish structural design values. If hardwood is intended to carry a structural load, confirm that it is permitted and specified for that use rather than relying on its appearance grade.
Also keep grade separate from size. A stamp does not certify a piece’s nominal dimensions or tell you whether its actual dimensions and span meet the design. Confirm both the lumber specification and the member requirements before installation.
Practical project scenarios
These illustrative scenarios show how to apply the chart without treating it as a substitute for plans or design checks. In each case, the right choice depends on the stated project requirements, the lumber’s complete stamp, and applicable rules—not on a grade name viewed by itself.
- A homeowner replacing a floor joist: The plans call for a named species group, grade, and size. The homeowner should check all three on the supplied lumber and confirm the required span and load details. A No. 2 board from a different species group is not automatically an acceptable replacement.
- A builder buying wall studs: The specification may call for Stud grade or another accepted grade. Check the plans and local code, because the Stud designation has different grading provisions from the Select Structural/No. 1/No. 2 sequence.
- A buyer choosing boards for a visible shelf: Appearance may be the main concern, but the board’s grade still does not prove that it can support a particular load. Check the product description and use requirements; do not treat a hardwood appearance grade as structural approval.
- A crew finding an unstamped board in a structural pile: Set it aside until its identity and grade are verified. Similar color, knots, or grain do not establish its species group or structural grade.
These examples are decision guides, not records of specific jobs. If a planned substitution changes species, grade, size, or moisture condition, get approval from the designer or other authority responsible for the project.
Inspection, storage, and grade verification
A grade stamp does not mean a piece is free of damage. Before use, inspect lumber for decay, damage, splits, excessive warp, and other conditions that could affect its intended role. A defect may matter differently depending on the member, location, and design, so do not make a structural approval based only on a quick visual check.
Keep wet and dry stock sorted when the project requires different moisture conditions. Store lumber so it is protected from avoidable moisture exposure and damage, following supplier and project guidance. Wood may shrink, swell, or change shape as its moisture content changes, so account for movement where the design or finish requires it.
A practical verification sequence is:
- Check the documents. Find the required species or species group, grade, size, moisture condition, and treatment.
- Read the stamp. Compare each marked detail with the specification, not just the grade.
- Inspect the piece. Look for damage or defects that may affect the planned use.
- Resolve uncertainty before installation. Ask the supplier or grading agency about unclear marks. Get approval before substituting species, grade, or size.
- Follow the design. Use the required fastening, bracing, treatment, and moisture-protection details.
The main takeaway is simple: use the stamp to identify the lumber, then use the plans and applicable design rules to decide where it belongs. Never use a general grade chart alone to size a structural member.
Frequently asked questions about lumber grades
These short answers clarify common questions about grade names, stamps, and substitutions. They are general guidance for U.S. lumber; the project documents, current grading rules, and applicable building code control when requirements differ.
Is No. 2 lumber strong enough for framing?
It can be used for framing when the specified species, grade, size, and design meet the project requirements. No. 2 by itself does not confirm that a member is suitable for a particular span or load.
Is Select Structural always stronger than No. 1 or No. 2?
It is a high structural stress grade in the common dimension-lumber sequence. But grade names alone do not compare all species, products, or grading rules. Check the applicable design values.
Can I replace No. 2 lumber with No. 3?
Not automatically. No. 3 permits more characteristics under its rules, and it is not a direct substitute for No. 2. Use it only when the project documents and applicable code permit it.
Does the same grade mean the same strength for every species?
No. Design values vary with species or species combination, grade, size, loading direction, and design conditions. Confirm the exact species group and use matching design values.
What does S-DRY mean on a lumber stamp?
S-DRY identifies surfaced dry lumber, generally at 19% moisture content or less at surfacing. It does not guarantee the piece will stay at that moisture level after delivery.
What is the difference between S-GRN and KD-19?
S-GRN generally identifies surfaced green lumber above 19% moisture content. KD-19 identifies lumber kiln-dried to a maximum moisture-content limit under the applicable grading rules.
Does a grade stamp prove that lumber is the right size for my project?
No. Grade and dimensions are separate. Verify actual dimensions and the required span, load, and member size in the project documents.
Can I use an appearance-grade hardwood for a beam?
An appearance grade does not directly establish structural design values. Use hardwood structurally only when the design and applicable rules specify or accept it for that purpose.
What should I do if a structural board has no readable stamp?
Do not assume its grade from appearance. Set it aside and ask the supplier or an authorized grading agency for verification before using it structurally.
Can I use this chart to size a beam or joist?
No. The chart explains common grade names, not member capacity. Use the plans, applicable building code, and current NDS design values, or consult a qualified building professional.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
