Lumber Grades

Lumber is a wood product, sawn and shaped from timbers of harvested trees. By its nature, wood is not of uniform consistency and therefore will contain defects that impact the appearance of the lumber that is created from the wood material, and which may impact the structural characteristics as well. In the U.S., lumber is assigned a grade which establishes a measure of consistency in the final products produced by mills. These grades are used to define both the quality of the lumber products delivered and to provide the buyer with a means to estimate the cost and waste associated with the selection of a given grade of the product as raw material.

There are grading systems for both softwood and hardwood lumber – this article presents a summary of both systems and the provides explanations of the meaning of each grade.

Softwood versus Hardwood

Woods may be classified as being either softwood or hardwood. However, those terms are not a strict indicator of the relative hardness of the wood itself.

Softwoods are those which are derived from the harvesting of coniferous trees (gymnosperms), which are more often known as evergreen trees. These trees are ones which usually have needles and cones as opposed to leaves. Softwood lumber tends to be lighter and has a lower density than hardwood, owing from the fact that these trees that exhibit a higher rate of growth than hardwood trees. The high rate of growth contributes to the abundant supply, with most of the processed timber coming from softwoods. They tend to have a straighter grain, making these woods suitable for use in construction framing lumber and building components such as windows and doors.

Some of the most commonly used softwoods that are created into lumber include:

• Cedar – both red and yellow most commonly

• Fir – often called Douglas Fir

• Pine

• Redwood

• Spruce

By contrast, hardwoods come from angiosperms (flowering trees which are usually broad-leaved), which lose their leaves in the fall and winter seasons. These trees contain vessels that serve as a transport mechanism for water, and exhibit pores on their surface which results in more intricate and interesting looking grains patterns in these woods, depending on the pore size. This characteristic makes them the choice woods for use in woodworking. Hardwood trees are slower growing than softwoods, which contributes to their higher density, making these woods stronger and more durable. This property lends to their use in furniture making, cabinetry, flooring, and other construction applications where longevity of service is of primary importance. Hardwood lumber is generally more expensive than softwood lumber, driven by a more limited supply from the slower rate of tree growth and the value of the strength of the material. 

Common hardwood lumber products include:

• Alder

• Ash including white ash

• Beech

• Birch

• Cherry

• Hickory

• Mahogany

• Maple

• Oak, including red and white varieties

• Poplar

• Teak

• Walnut

Table 1 below summarizes the common hardwood and softwood varieties and their density in pounds per cubic foot.

Table 1 – Density of Common Hardwoods and Softwoods

Softwood Lumber Grades

The American Lumber Standard Committee (http://www.alsc.org) serves as the body that developed and maintains the American Softwood Lumber Standard PS 20 under auspices of the U.S. Department of Commerce.

The majority use case for softwood lumber is for what is characterized as construction lumber, which may be further subdivided into stress-graded, nonstress-graded, and appearance lumber. Appearance lumber is judged mainly by the overall visual quality, whereas stress-graded or nonstress-graded lumber is more concerned with the structural integrity of the wood. Retail lumberyards typically sell nonstress-graded and appearance lumber, which is collectively referred to as “yard lumber”. Grading is done after the drying and surfacing operations are completed and is accomplished based on both the size and number of defects appearing on the better side of the piece.

Nonstress Lumber Grades

For nonstress lumber pieces (a common example being the “2-by”) which is less than 2” thick and greater than nominal 2” in width, the grades are shown in Table 2 below:

Table 2: Lumber Grades for Common (nonstress-graded) Lumber

Appearance Lumber Grades

With appearance lumber, there is additional emphasis on the physical look of the lumber given that it may be exposed once installed, e.g. used to make softwood furniture. The highest grade of appearance lumber is designated as finish, followed by selects and common. There is some variation in these terms and grades depending on the agency responsible.

Table 3 below shows the grade designations for select and common softwoods:

Table 3: Lumber Grades for Select and Common Appearance Lumber

Stress-Graded Lumber Grades

Softwoods that are stress-graded are used as beams, posts, studs, rafters, and joists, for example, where the material is functioning in a load-bearing capacity and working stresses will be applied. The stress gradings may be determined either by visual means or through mechanical testing according to ASTM standards and procedures, establishing standard working values for mechanical properties such as the modulus of elasticity and the bending moment. These pieces are referred to as structural lumber.

Stress-graded lumber grading is shown below in Table 4:

 Table 4: Lumber Grades for Stress-Graded Lumber

Hardwood Lumber Grades

Grading of hardwoods is significantly less complicated than that of softwoods. The American Hardwood Export Council (https://www.ahec.org/) has developed The Illustrated Guide to American Hardwood Lumber Grades which provides the basis for the grading system, measurement standards, and descriptions of the characteristics and defects associated with the ten of the common hardwoods in use.

Given the emphasis with hardwoods on the overall appearance of the product, it should not be surprising that appearance becomes the primary factor used to establish the grade of the lumber. Hardwood grading for lumber considers the size and number of pieces (or cuttings) which may be yielded during the creation of a hardwood product. The grading system is based, therefore, on the measurable percentage of clear wood that is defect-free for each of the grades. The higher grades will have a larger percentage of usable material yield, which declines steadily for the lower grades of hardwood. So, the highest grades provide the largest or longest clear pieces for use, while the lower or common grades require additional cuts to obtain clear pieces, which thereby will tend to be shorter or smaller.

The upper or highest grades are designated as FAS (Firsts and Seconds), FAS/1F (FAS-One-Face) and Sel (Selects). These are most suitable for applications such as furniture, long clear moldings, and other product use where there is a necessity for ling wide cuttings that are as clear as possible.

The common grades, Number 1 Common and Number 2 Common, are suitable for kitchen cabinetwork, furniture parts, and plank and strip flooring. Note that the grade difference between the upper and common grades reflects the yield (measured as the usable % of the material that is clear and defect-free). The clarity of the common piece will be the same as that of the upper grade, but the size will be smaller for the common compared with the FAS and Select grades.

Firsts and Seconds grade (FAS)

Firsts and Seconds grade (FAS) grade requires:

• a minimum board size of 6” x 8”

• a length of 8’ or longer

• a yield of 83-1/3% to 100% clear wood cuttings

• a minimum cutting size of 3” wide x 7’ long or 4” wide x 5’ long

• that both sides of the board must meet the requirements

FAS One Face (F1F) grade calls for the piece to meet the FAS grade requirements for the so-called better face of the board, while the poor face can meet the requirements of the lower number 1 common grade. This grade is often mixed with FAS when sold in an agreed-upon percentage such as 80% FAS / 20% F1F.

Selects Grade

The requirements for selects are the same as for the F1F, except that the minimum board size is reduced to 4” and wider with lengths 6’ or longer.

Number 1 Common (No. 1C) Grade

The Number 1 Common grade, also called cabinet grade, is used to produce kitchen cabinets and furniture parts. The Number 1 Common grade requires call for:

• a minimum board size of 3” wide

• a minimum length of 4’ long

• a clear face yield of 66-2/3% up to, but less than, the FAS minimum yield of 83-1/3%

• a minimum clear-cutting size of 3” x 3’ or 4” x 2’

• a requirement that both faces of the board achieve these standards

Number 2A Common (No. 2AC)

Number 2A Common grade, referred to as Economy grade, further reduces yields and board sizes. This grade is often selected for use by the hardwood flooring industry, and also finds application for the manufacturing of furniture components that are small. The Number 2A Common grade requires:

• a minimum board size of 3” wide

• a minimum length of 4’ long

• a clear face yield range of 50% minimum up, but less than, the Number 1 Common yield limit of 66-2/3%

• a minimum clear-cutting size of 3” x 2

• the grading to be based on the poorest face

So even the better face would achieve a higher grade, the piece will still be rated at the Number 2A Common grade.

A summary of the grade designations appears in Table 5 below:

Table 5: Lumber Grades for Hardwoods

Useful Nomenclature

There are specific terms and definitions that are used in the grading of lumber, a few of which are summarized here for convenience:

Board foot – defined as the product of the width of the board by the thickness (both in inches) multiplied by the length of the board in feet.

Surface measure – defined as a measure of the surface area of the board. Surface measure is calculated by taking the product of the width of the board (measured in inches) by the length of the board (measured in feet) and then dividing that product by 12, rounding to the nearest whole number value. This measure is the estimated surface area in square inches.

Gross tally – also called green tally, this value represents the number of board feet of kiln-dried lumber when measured prior to the drying process. Shrinkage from the drying operation will reduce this value by approximately 7%

Net tally – the same measurement as gross tally, except that the measurement is performed after the drying operation is performed on the lumber.

Summary

This article presented a summary of the different grading systems for softwoods and hardwoods. To learn more about the suppliers of lumber, see our guide to lumber suppliers in the U.S.

To explore other topics, consult our additional guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.

Sources:

1. https://www.esf.edu/wus/documents/IllustratedGradingGuide.pdf

2. http://www.woodbin.com/ref/softwood-grades/

3. https://www.easybiologyclass.com/difference-between-hardwood-and-softwood/

4. https://www.diffen.com

5. https://www.engineeringtoolbox.com

6. https://classes.mst.edu

7. https://www.wwpa.org/western-lumber/structural-lumber/dimensional-lumber