Lumber Terminology

The lumber and woodworking industries have some abbreviations and technical terms that can be confusing. We’ve put together this short list of important terms to make the craft more accessible.

BF — Board Foot is the standard unit of measurement for lumber volume. Most of our lumber is sold by the board foot rather than the linear or square foot. A board foot is a measurement for a piece of lumber 12" wide by 12” long by 1" thick. Measuring in inches, the standard formula for calculating board footage is (width x length x thickness) ÷ 144.

COM — Common-grade lumber does not contain many defects, but knots are allowed as long as they are well-spaced and within size regulations.

FAS — Firsts and Seconds is the highest grade of lumber. FAS grade includes few defects and is considered the best lumber for applications like furniture and cabinet-making.

H/M — Hit-and-Miss or skip-planed lumber refers to rough lumber that has been lightly surfaced to reveal and highlight woodgrain that might otherwise be difficult to see.

KD — Kiln-Dried lumber has been dried in a temperature-controlled kiln to a specific moisture level and is therefore ready to work—no further air-drying necessary. All of our lumber is kiln-dried and ready to go!

RGH — Rough lumber is sold like it just it came off the saw. Rough material has not been surfaced by a planer.

RTWL — Random Thickness, Width and Length refers to a stack of lumber that has an assortment of boards with varying thickness, width and length measurements. Most of our lumber is stacked in units of similar thickness and length, though width measurements may vary from board to board.

S2S — Surfaced on 2 Sides refers to lumber that has been run through a planer to give it two flat faces; the edges are left rough.

S4S — Surfaced on 4 Sides refers to lumber that has been run through a planer to give it four flat surfaces (both faces and edges).

SLR — Straight Line Ripped lumber is material that has been given a straightened edge with a saw.

4/4, 5/4, 8/4, etc. — “Four-quarter,” “Five-quarter,” “Eight-quarter” and so on are industry-standard measurements for rough-cut board thickness. 4/4 = 1”; 5/4 = 1.25”; 8/4 = 2” thick. When rough material is surfaced, however, it typically loses about .25” in thickness. This means that surfaced material listed as “4/4” will actually measure about 0.75” in thickness, “5/4” will actually measure about 1”, “8/4” will actually measure about 1.75” and so on.