Many factors determine the grade of a piece of lumber including:
  • Bark on edges
  • Machining defects
  • Species
  • Number, size, and position of knots and holes
  • Decay
  • Bowing, warping, and twisting
     The U.S. Department of Commerce establishes the rules for grading. The rules are maintained by the American Lumber Standards Committee (United States). These standards are enforced by regional organizations such as (Western Wood Products Association, Southern Pine Inspection Bureau, California Inspection Service, and others).
The following cross-sectional dimensions define the different categories of lumber:
  • Boards: 1" to 1-1/2" thick, 2" and wider.
  • Dimension Lumber: 2" to 4" thick, 2" and wider.
  • Timbers: 5" and thicker, 5" and wider.
     Lumber is graded for strength and for appearance, in general most boards (1-by's) are graded for appearance and most dimension lumber is (2-by's) are graded for strength.  Lumber is graded for allowable defects - how bad it looks, not how good it looks. This is true whether it's being graded for appearance or for strength.
[Hardwood Lumber][Structural Framing Lumber][Boards]

Structural Framing Products
     The following will explain what the grades of lumber are, the characteristics of each grade, and what is the highest grade of lumber to the lowest. Grade stamps will also be explained and how to read the information contained in a grade stamp.
Dimension Lumber grades from highest to lowest.
  • Select Structural
  • No. 1 & BTR (DF-L, DF & Hem-Fir species only)
  • No. 2
  • Construction
  • No. 3
  • Stud
  • Standard
  • Utility
The descriptions of the grades are taken from the Western Wood Products Association Lumber Grading Rules 98. This is just a sampling of the grading rules to give you an idea of how a piece of lumber is graded and why.
Not all characteristics are listed!
If you would like the grading rules you can go to the Western Wood Products Association website to order a copy of the Grading Rules
Structural Joists & Planks
     The National Grading Rule for Dimension Lumber contains four grades of Structural Joists and Planks: SELECT STRUCTURAL, NO. 1, NO. 2, and NO. 3. All are graded full length. Knots appearing on narrow faces are limited to the same displacement as knots specified at edges of wide faces.

Select Structural
2" to 4" Thick
5" and Wider
Checks - Surface seasoning checks, not limited. Through checks are limited as splits. Shake - If through at ends, limited as splits. Surface shakes up to 2' long. Skips - Hit and miss skips in a maximum of 10% of the pieces. Splits - Equal in length to the width of the piece. Wane - 1/4 the thickness and 1/4 the width full length, or equivalent on each face, provided that wane not exceed 1/2 the thickness or 1/3 the width for up to 1/4 the length. Knots - Sound, firm, encased, and pith knots, if tight and well spaced, are permitted in sizes not to exceed the following, or equivalent displacement.
Nominal Width At Edge Wide Face Centerline Wide Face Unsound or Loose Knots & Holes
6" 1-1/8" 1-7/8" 1"
8" 1-1/2" 2-1/4" 1-1/4"
10" 1-7/8" 2-5/8" 1-1/4"
12" 2-1/4" 3" 1-1/4"
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No. 1
2" to 4" Thick
5" and Wider
Checks - Surface seasoning checks, not limited. Through checks are limited as splits. Shake - If through at ends, limited as splits. Surface shakes up to 2' long. Skips - Hit and miss skips in a maximum of 10% of the pieces. Splits - Equal in length to the width of the piece. Wane - 1/4 the thickness and 1/4 the width full length, or equivalent on each face, provided that wane not exceed 1/2 the thickness or 1/3 the width for up to 1/4 the length. Knots - Sound, firm, encased, and pith knots, if tight and well spaced, are permitted in sizes not to exceed the following, or equivalent displacement.
Nominal Width At Edge Wide Face Centerline Wide Face Unsound or Loose Knots & Holes
6" 1-1/2" 2-1/4" 1-1/4"
8" 2" 2-3/4" 1-1/2"
10" 2-1/2" 3-1/4" 1-1/2"
12" 3" 3-3/4" 1-1/2"
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No. 2
2" to 4" Thick
5" and Wider
Checks - Surface seasoning checks, not limited. Through checks are limited as splits. Shake - If through at ends, limited as splits. Away from ends through shakes up to 2' long, well separated. If not through, single shakes shall not exceed 3' long or 1/4 the length, whichever is greater. Skips - Hit and miss skips with a maximum of 5% of the pieces containing hit or miss or heavy skip 2' or less in length. Splits - Equal in length to 1-1/2 times the width of the piece. Wane - 1/3 the thickness and 1/3 the width full length, or equivalent on each face, provided that wane not exceed 2/3 the thickness or 1/2 the width for up to 1/4 the length. Knots - Well spaced knots of any quality are permitted in sizes not to exceed the following or equivalent displacement:
Nominal Width At Edge Wide Face Centerline Wide Face Unsound or Loose Knots & Holes
6" 1-7/8" 2-7/8" 1-1/2"
8" 2-1/2" 3-1/2" 2"
10" 3-1/4" 4-1/4" 2-1/2"
12" 3-3/4" 4-3/4" 3"
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No. 3
2" to 4" Thick
5" and Wider
Checks - Seasoning checks not limited. Through checks are limited as splits. Shake - Surface shakes permitted. If through at edges or ends, limited as splits. Elsewhere, through shakes 1/3 the length, scattered along the length. Skips - Hit or miss, with a maximum of 10% of the pieces containing heavy skips. Splits - Equal 1/6 the length of the piece. Wane - 1/2 the thickness and 1/2 the width full length, or equivalent on each face, provided that wane not exceed 7/8 the thickness or 3/4 the width for up to 1/4 the length. Knots - Well spaced knots of any quality are permitted in the following sizes or their equivalent displacement:
Nominal Width At Edge Wide Face Centerline Wide Face Unsound or Loose Knots & Holes
6" 2-3/4" 3-3/4" 2"
8" 3-1/2" 4-1/2" 2-1/2"
10" 4-1/2" 5-1/2" 3"
12" 5-1/2" 6-1/2" 3-1/2"
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LIGHT FRAMING
     The National Grading Rule for Dimension Lumber contains three grades of Light Framing: CONSTRUCTION, STANDARD, and UTILITY. All are graded full length. Except as provided in the grade descriptions, knots appearing on narrow faces are limited to the same displacement as knots specified for the wide face.
Construction
2" to 4" Thick
2" to 4" Wide
Checks - Surface seasoning checks, not limited. Through checks at ends are limited as splits. Shake - If through at ends, limited as splits. Surface shakes up to 2' long. Skips - Hit and miss skips in a maximum of 10% of the pieces. Splits - Equal in length to the width of the piece. Wane - 1/4 the thickness and 1/4 the width full length, or equivalent on each face, provided that wane not exceed 1/2 the thickness or 1/3 the width for up to 1/4 the length. Knots - Sound, firm, encased, and pith knots, must be tight and are permitted in the following sizes or their equivalent displacement.
Nominal Width Anywhere on Wide Face Unsound or Loose Knots & Holes
2" 3/4" 5/8"
3" 1-1/4" 3/4"
4" 1-1/2" 1"
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Standard
2" to 4" Thick
2" to 4" Wide
Checks - Seasoning checks not limited. Through checks at ends are limited as splits. Shake - If through at ends, limited as splits. Away from ends through shakes up to 2' long, well separated. If not through, single shakes shall not exceed 3' long or 1/4 the length, whichever is greater. Skips - Hit and miss with a maximum of 5% of the pieces containing hit or miss or heavy skip 2' or less in length. Splits - Equal in length to 1-1/2 times the width of the piece. Wane - 1/3 the thickness and 1/3 the width full length, or equivalent on each face, provided that wane not exceed 2/3 the thickness or 1/2 the width for up to 1/4 the length. Knots - Not restricted as to quality and are permitted in the following sizes or their equivalent displacement.
Nominal Width Anywhere on Wide Face Unsound or Loose Knots & Holes
2" 1" 3/4"
3" 1-1/2" 1"
4" 2" 1-1/4"
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Utility
2" to 4" Thick
2" to 4" Wide
Checks - Seasoning checks not limited. Through checks at ends are limited as splits. Shake - If through at ends, limited as splits. Away from ends through shakes up to 2' long, well separated. If not through, single shakes shall not exceed 3' long or 1/4 the length, whichever is greater. Skips - Hit or miss with a maximum of 10% of the pieces containing heavy skips. Splits - Equal to 1/6 times the length of the piece. Wane - 1/2 the thickness and 1/2 the width full length, or equivalent on each face, provided that wane not exceed 7/8 the thickness or 3/4 the width for up to 1/4 the length. Knots - Not restricted as to quality and are permitted in the following sizes or their equivalent displacement.
Nominal Width Anywhere on Wide Face Unsound or Loose Knots & Holes
2" 1-1/4" 1"
3" 2" 1-1/4"
4" 2-1/2" 1-1/2"
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STUDS
     The National Grading Rule for Dimension Lumber contains one STUD grade.It is graded full length. Knots appearing on narrow faces are limited to the same displacement as knots specified for the wide face.
Stud
2" to 4" Thick
2" and Wider
Checks - Seasoning checks not limited. Through checks at ends are limited as splits. Shake - If through at ends, limited as splits. Elsewhere, through shakes 1/3 the length. Skips - Hit or miss on any face, with a maximum of 10% of the pieces containing heavy skips on wide faces only. Splits - Equal in length to twice the width of the piece. Wane - 1/3 the thickness and 1/2 the width full length, or equivalent on each face, provided that wane not exceed 1/2 the thickness and 3/4 the width for up to 1/4 the length. Knots - Not limited as to quality but are well spaced and are permitted in the following sizes or their equivalent displacement.
Nominal Width At Edge Wide Face Centerline Wide Face Unsound or Loose Knots & Holes
4" 1-3/4" 2-1/2" 1-1/2"
6" 2-3/4" 3-3/4" 2"
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Hardwood Lumber Grading
     The National Hardwood Lumber Association establishes the standards for hardwood grading in the United States. The standards are voluminous, with exceptions, with special rules for certain species, and many details. What follows are the principles behind the grading.  Hardwood is usually used in applications where appearance is crucial. Wood is a natural product, therefore no two boards are alike and almost certain to contain defects like knots that would be unacceptable in a piece of furniture. In most cases only one side of the board will show. The grading of hardwood reflects that. Hardwood grading is based on the number and size of the clear face cuttings {rectangular pieces free of defects on the graded side} that could be cut from the board being graded. The other side of a clear face cutting may contain defects as long as they don't affect the boards strength. Grading a board doesn't involve actually sawing the clear face cuttings from it; they are purely conceptual.
Grades
     Hardwood lumber grades as defined by the U.S. National Hardwood Lumber Association (in descending order of quality) are Firsts, Seconds, No. 1 Common, No. 2A Common, No. 2B Common, Sound Wormy, No. 3A Common, and No. 3B Common. Some of the above grades are rarely used commercially and others are typically combined. For example, Firsts and Seconds are usually combined into one grade: "FAS", No. 1 Common and Selects are grouped as No. 1 Common and Better, and No. 2A Common and No. 2B Common may be combined as No. 2 Common. The grade of Sound Wormy is rarely used commercially.
  • Firsts and Seconds (FAS)
The best and most expensive grade, suitable for applications where clear, wide boards are required. In a lot of boards graded FAS 20 to 40 percent of the boards must be Firsts (actual percentage depends on the species). Boards must be at least 6" wide and from 8' to 16' long; In a lot of boards 30 percent of the boards can be shorter than 11', and only half of those boards can be 8' or 9' in length. FAS grading is based on the poorest side of the board. Yields 83-1/3 percent clear face cuttings.
  • 1 Face (1F)
The 1F grade is almost always grouped together with the FAS grade. The 1F grade is obtained by grading both faces of the board. The best face must meet the requirements of an FAS grade, while the poorer face must meet the grade requirements of a #1 Common grade.
  • Selects
Face side is FAS, back side is No. 1 Common. Boards are 4" and wider, 6' and longer. Yields 83-1/3 percent clear face cuttings. A cost effective substitute for FAS when only one good face is needed. The select grade is essentially the same as the 1F grade, except for the minimum board size. Select grades minimum board size after kiln drying is 3-" wide by 6' long.
  • No. 1 Common
Boards are 3" and wider, 4' and longer. Yields 66-2/3 percent clear face cuttings. Provides good value, especially if small pieces can be used.
  • No. 2A & 2B Common
Boards are 3" and wider, 4' and longer. Yields 50 percent clear face cuttings. Suitable for some paneling and flooring applications.
  • Sound Wormy
Same requirements as No. 1 Common and better but wormholes, limited sound knots, and other imperfections allowed. Not commonly available.
  • No. 3A Common
Boards are 3" and wider, 4' and longer. Yields 33-1/3 percent clear face cuttings. Economical choice for pallets, fencing, and crates.
  • No. 3B Common
Boards are 3" wide, 4' and longer. Yields 25 percent clear face cuttings. Same applications as 3A Common.
FAS, 1F, Selects, and No. 1 Common are the top grades available in the retail market place. The remaining grades - 2A, 2B, 3A, and 3B rarely reach the retail market.
Hardwood Lumber Grade Chart
Grade Minimum Board Length Minimum Board Width Minimum Cutting Size Min. Area of Clear Cuttings Required
FAS 8' 6" 4"x 5'/3"x 7' 83-1/3%
Selects 6' 4" 4"x 5'/3"x 7' 83-1/3%
No.1 Common 4' 3" 4"x 2'/3"x 3' 66-2/3%
No.2 Common 4' 3" 3"x 2' 50%
No.3A Common 4' 3" 3"x 2' 33-1/3%
No.3B Common 4' 3" 1-1/2"x 2' 25%
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Common Boards
The five common board grades are:
  • #1 Common
  • #2 Common
  • #3 Common
  • #4 Common
  • #5 Common

#1 Common
Lumber of this grade is used when the ultimate in fine appearance of knotty material is required. This grade includes all sound, tight-knotted stock with the size and character of the knot the determining factor of the grade. Checks - Four small surface seasoning checks in a 1" x 8" x 12'. Skip - Three very light skips on one edge or two light on back in a 1" x 8" x 12'. Split - Very short splits, limited to one on each end. Wane - On back, 1/2 thickness, 1/8 width, 1/4 length in occasional pieces. Knots - Sound tight knots and smooth red knots limited as follows:
Face Width Knot Size
2" 5/8"
3" 7/8"
4" 1-1/4"
6" 1-3/4"
8" 2-1/4"
10" 2-1/2"
12" 2-3/4"
14" & wider 3"
The knot sizes listed above will generally be the maximum size found in this grade. However , there may be pieces of otherwise exceptional quality which may contain slightly larger knots than those shown.
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#2 Common
Lumber of this grade is intended primarily for use in housing and light construction where it is exposed as in paneling, shelving and other uses where a knotty type of lumber with fine appearance is required. Checks - Two medium seasoning checks or equivalent smaller 1" x 8" x 12'. Light roller checks on back not more than 1/4 the length. Skip - Medium skip on back limited to 1/4 of the length, medium on edge limited to 1/3 of length. Split - Short splits, limited to one on each end. Wane - On back, 1/2 thickness, 1/6 width, 1/3 length or equivalent in an occasional pieces. Knots - Knots are limited as follows:
Face Width Red Knots Sound and Tight Black Knots Sound and Tight
2" 1" 3/8"
3" 1-1/4" 1/2"
4" 2" 3/4"
6" 2-1/2" 1"
8" 3" 1-1/4"
10" 3-1/4" 1-3/8"
12" 3-3/4" 1-1/2"
14" & wider 4" 1-3/4"
The knot sizes listed above will generally be the maximum size found in this grade. However , there may be pieces of otherwise exceptional quality which may contain slightly larger knots than those shown.
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#3 Common
Lumber of this grade is widely used for a large range of building purposes where appearance and strength are both important. This grade is often used for shelving, paneling, and siding and is especially suited for fences, boxes, crating, sheathing, and many industrial uses. Checks - Medium seasoning checks. Roller checks. Skip - One medium skip on face, hit and miss skips on back for 2/3 the length. One edge may have 1/8" skip for 1/2 the length or 1/16" skip full length. Split - 1/6 the length. Wane - On back, 2/3 thickness, 1/4 width, 1/2 length or equivalent in an occasional pieces. Knots - Knots are limited as follows:
Face Width Fixed Knots Firm and Tight Knots Loose Knots and Knotholes
2" 1-5/16" 3/4"
3" 1-3/4" 1"
4" 3" 1-1/2"
6" 3-1/2" 2"
8" 2/3 width 2-1/2"
10" 2/3 width 3"
12" 2/3 width 3-1/2"
14" & wider 2/3 width 4"
The knot sizes listed above will generally be the maximum size found in this grade. However , there may be pieces of otherwise exceptional quality which may contain slightly larger knots than those shown.
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#4 Common
Lumber of this grade is more widely used than other grades for general construction purposes. Boards of this grade are used for sub-floors, roof and wall sheathing, concrete forms, low cost fencing, and crating. Although appearance is given consideration, pieces are graded chiefly for serviceability, as they are seldom used in exposed construction. Checks - Large seasoning checks. Medium to heavy roller checks full length on back, light to medium 2/3 on face. Skip - Hit and miss skip on face, 1/16" skip full length if surfaced one side. One edge may have 1/4" skip for 1/2 the length or 1/8" skip full length. Split - 1/3 the length. Wane - 1/2 thickness, 1/8 width, 1/6 on face. Heavy wane on back, but equivalent to knot holes if through thickness. Knots - Knots are limited as follows:
Face Width Fixed Knots Firm and Tight Knots Loose Knots and Knotholes
2" 1-5/16" 3/4"
3" 1-3/4" 1"
4" 3" 1-1/2"
6" 3-1/2" 2"
8" 2/3 width 2-1/2"
10" 2/3 width 3"
12" 2/3 width 3-1/2"
14" & wider 2/3 width 4"
Knot holes and/or loose knots of maximum size are limited to three for each 12' length.
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#5 Common
Lumber of this grade is intended for use in construction where lumber of a higher grade is not needed. This grade permits characteristics such as stain, large knots, very large holes, unsound wood, massed pitch, heavy shake, splits and wane in varying stages or degrees singly or in combination. Many pieces in this grade are only slightly lower than the #4 Common grade while others will be at the opposite end of the grade level. Although #5 Common is the lowest Common Board grade, it is suitable for uses in economical construction where appearance and strength are not basic requirements.
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Select Boards
The three Select board grades are:
  • B & BTR
  • C Select
  • D Select

     In Select grades, all pieces are graded from the better side or face. The reverse side may be somewhat lower in quality with more restrictions placed on the back of the higher grades.
B & Better Select
Lumber of this grade may be ordered when the ultimate in fine appearance is desired. This is the highest grade of Select lumber produced and many pieces are absolutely clear. Some pieces may have a few minor characteristics which do not detract from their appearance or high quality. Checks - Small seasoning checks, one on each end, or three or four if away from ends. Skip - Very light skip on one edge light skip on back. Wane - On reverse side only, 1/4 the thickness, 1/6 the length in an occasional piece. Any one of the following characteristics or equivalent. Knots - Two pin, sound, tight knots. Pitch - Slight traces. Pocket - One very small pocket.
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C Select
Lumber of this grade is recommended for all finishing uses where fine appearance is essential. Because its appearance and usability ranks only slightly less than B & BTR., it is one of the most sought after products from the clear portion of the log. It is widely used for high quality interior trim. Checks - Small well scattered seasoning checks on the surface. Skip - Light skip on one edge, one medium or two light skips on the back. Wane - On reverse side 1/2 the thickness, 1/8 the width, 1/4 the length in an occasional piece. Any one of the following characteristics. Knots - Two small, sound, tight knots. Pitch - Light pitch over not more than 1/2 the face. Pitch Streak - One small pitch streak. Pocket - Two very small pocket. Equivalent characteristics no more damaging than any of the above.
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D Select
Lumber of this grade has many of the fine appearance features of C Select grade. Although generally less restrictive than C Select, D Select is suitable where the requirements for finishing are less exacting. Checks - Small, scattered seasoning checks, medium checks on back. Skip - One very light skip on face, hit and miss skip on back; one edge may have 1/16" skip for 1/2 the length in an occasional piece. Wane - On reverse side, 3/4 the thickness, 1/4 the width, 1/4 the length. Any one of the following characteristics. Knots - Four small fixed knots. Pitch - Medium pitch over not more than 2/3 of face, less if heavy. Pitch Streak - One medium pitch streak. Pocket - Four small pockets. Equivalent characteristics no more damaging than any of the above.
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