Lumber Dimensions & Definitions

Lumber Dimensions are confusing.

This page should help clear the air on lumber dimensions.

Normally, hardwood is stated in quarters, i.e. 4/4 = 1" (pronounced four quarter, 5/4 = 5 quarter). In other words, 4-quarter (4/4) equals 1" thick, 5/4 equals 1¼" thick, 6/4 equals 1½" thick, etc.

Usually, you buy in Board-Feet. A board-foot is 144 cubic inches. You calculate board feet by multiplying (inches) length x width x thickness and divide by 144". A piece of lumber 96"L x 6"W x 1½"T = 864" divided by 144" = 6 board-feet.

Board footage is calculated on lumber prior to surfacing, and often prior to drying. When buying planed Hardwood, sizing is more confusing. It depends on S1S (surfaced on one side) or S2S (surfaced on two sides. Even S4S Lumber (surfaced 4 sides) is sanded on one side only.


When you buy planed wood from the Home Centers, the 4/4 board is only 3/4" thick. If the width states 6", it may only be 5½". You are paying for waste.

Where to buy quality hardwood.

This link takes you to a quality lumberyard that sells direct to you. You can order special thickness by request, and they provide oversized lengths. There shipping costs are most reasonable. They give net lumber dimensions as well: Quality Lumberyard


FAS (First and Seconds)
Provides long, wide, clear cuttings. Best suited for high quality work. Must yield 83 1/3% to 100% clear wood in cuttings at least 3" x 7' or 4" to 5'.

Select & Better
Both faces of the board are used in determining the grade. Best face must meet FAS, reverse must Grade to No. 1 Common.

No. 1 Common
Provides clear cuttings of medium length and width. Includes a range of boards which will yield from 66 2/3% to 83 1/3% clear wood in minimum sized cuttings at least 3" x 3' or 4" x 2'.

ANSI Plywood Grading Standards

Plywood is graded with a two-character stamp, such as A-1, B2, etc.
The grades reflect the quality of the face veneer and back veneer. The descriptions of the ANSI grading standards follow:

Face Grade Back Grade
Where excellent appearance is very important, as in cabinets and furniture.
Provide sound surfaces with all openings in the veneer repaired except for vertical worm holes not large than 1/16"
Where the natural characteristics and appearance of the species are desirable.
Some open defects. Repaired splits, joints, bark pockets, laps and knotholes can achieve a sound surface, if specified by the buyer.
Provide sound surfaces but allow unlimited color variations. Repairs in increasing size ranges allowed.
Use for hidden surfaces.
Some open defects. Knotholes up to 4" diameter are permitted. Open splits, and joints limited by width and length.


Hardwood Lumber grades are objective. There are no "gray" areas from the high end of one grade to the low end of the next higher grade.

Plywood grading is a visual standard. It becomes subjective from one plywood grader to another. Grading rules use terms like "blending, inconspicuous, occasional, slight and sharp contrast". This makes for "gray" areas. There is always some degree of overlap in appearance from the top of one grade and the bottom of the next higher grade.

Wood Tip

I would not use much below A1-2 for anything. Otherwise, you can have trouble down the road.

Since plywood is getting thinner by the year, you may want to consider resawing solid wood to size. Then use tongue & groove to edge joint a solid piece. You make solid table/desk tops that way. You will see an easy technique to center edge joints on Center Edge-to-Edge Joints near the center of the page.

Be careful of lumber dimensions when searching for wood.

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