What is a board foot?

A board foot is a unit of measure equal to the board’s thickness times its width times its length, divided by 12. For example, a board 1″ thick, 4″ wide and 3′ long is 1 board foot (bf).

1 x 4″ x 3′ / 12 = 1 bf

How do I calculate board feet?

For domestic lumber, you can calculate board feet in inches or in feet. Use one of these two formulas to calculate board feet. Rounding up the total to the nearest quarter of a foot is standard industry practice (e.g., 3.8 bf becomes 4 bf).

Formula Example

1. T” x W” x L” /144 = bf

Ex. 1″ x 6″ x 96″ = 4 bf

2. T” x W” x L’ / 12 = bf

Ex. 1″ x 6″ x 8′ / 12 = 4 bf

(T = thickness, W = width, L = length, bf = board feet)

For exotic lumber, standard measurement is by the inch (length only?) and calculated to two decimal places.

What is “S4S”?

A typical lumber yard or home center sells softwood and hardwood lumbers called S4S (surfaced four sides). Material has been milled away on all four sides to a specific size. These boards are sold by the linear (running) foot. What is sold as a 1″ x 6″ is actually 3/4″ x 5-1/2″ in true measure. (The price includes all material milled away and the labor involved in milling boards to a specific size.)

On the other hand, at a lumber dealer, who sells by the board foot, all lumber is not milled the same, so you end up getting more of the material you’re paying for.

When buying lumber by the board foot, the boards may be in any number of milled stages. Some may be completely rough, as when they came from the sawmill. Others may have one straight, milled edge and be surfaced on two sides (S2S) to a thickness typically greater than the usual finished thickness. (See the chart.)

Regardless of how much milling has been done, lumber sold by the board foot is more economical than S4S lumber.

What do 4/4, 5/4, 6/4, etc., mean?

The thickness of hardwood lumber is measured in quarters of an inch. So a 4/4 (four- quarters) would be 1″. This is the thickness before surfacing and the number you use to calculate board feet. This is also the thickness you pay for, even though, after planing, the thickness may be only 3/4″. The chart shows the typical thickness for hardwood lumber before and after planing. (What is softwood?)

Rough Thickness

4/4 = 1″ 13/16″ 3/4″

5/4 = 1-1/4″ 1-1/16″

6/4 = 1-1/2″ 1-1/4″

8/4 = 2″ 1 3/4″ 1-1/2″

4/4 (four-quarter) lumber is 1″ thick when rough sawn. When 4/4 lumber is planed, it is typically finished at 13/16″ thick.

5/4 (five-quarter) lumber is 1.25″ thick when rough sawn. When 5/4 lumber is planed, typically it is finished at 1.063″ thick.

6/4 (six-quarter) lumber is 1.5″ thick when rough sawn. When 6/4 lumber is planed, typically it is finished at 1.25″ thick.

8/4 (eight-quarter) lumber is 2″ thick when rough sawn. When 8/4 lumber is planed, typically it is finished at 1.75″ thick.

12/4 (twelve-quarter) lumber is 3″ thick when rough sawn. When 12/4 lumber is planed, typically it is finished at 2.75″ thick.

16/4 (sixteen-quarter) lumber is 4″ thick when rough sawn. When 16/4 lumber is planed, typically it is finished at 3.75″ thick.

What is “R1E”?

R1E stands for ripped on one edge. This edge is straight enough to accept a glue joint.

Typically, R1E stock has not been surface planed.

KenCraft will “clean up” any rough-sawn lumber for $0.20/bf. 1/16″ will be taken off both sides.

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