Computation of board feet and price

Board feet is often abbreviated bd ft. A board foot is a piece of lumber 1 in. thick by 12 in. long and 12 in. wide or 1 in X 12 in. X 1’ – 0” (or other combinations of dimensions that total 144 cubic inches). Lumber thinner than 1 in. is still calculated at the 1-in. thickness, while lumber over 1 in. thick is calculated in multiples of 1/4 in. up to 2 in. thickness. Another common abbreviation used is RW&L or simple RWL meaning “random width and length”, which applies to selection of the pieces in a lumber order. Ordering specific lengths will mean a slight additional charge for selecting the specified lengths, and one always pays for a full foot of length. Calculating a problem in board feet is a rather simple arithmetic process and should not be mysterious with a bit of practice. The basic formula for calculating the number of board feet is:

No. pieces X width (in.) X thickness (in.) X length (ft.) / 12

Example 1:
10 pcs. – 2 X 4 – 10 ft long / 12

Calculation:
10 X 2 X 4 X 10 = 800
800 / 12 = 66 2/3 bd. ft.

Example 2:
Three pieces of oak are ordered 1 X 8 – 12 ft. long

Calculation:
3 – 1 X 8 – 12 / 12 = 24 bd. ft.

(Note: where 12 appears both above and below the formula line, they can be canceled out and the remaining numbers multiplied.)

Practical retail usage rounds off the fractional portion of a board foot to the nearest whole foot using the standard round-off rules: less than half of a foot, drop it; half or over go up to the next foot.

Lumber thicker than 1 in. is designated by adding quarters to the standard 1 in. Thus lumber measuring 1 1/4 in. thick is called five quarter, 1 1/2 in. thick is known as six quarter, 1 3/4 in. is seven quarter and 2 in. is eight quarter. To calculate the cost of lumber measuring five quarter in thickness, simply calculate the number of board feet using the formula for the 1 in. thickness and then add 1/4 , 1/2 , or 3/4 or more. Thus 6 pieces 5/4 X 8 – 12 ft. long is figured

6 pcs. – 1 X 8 – 12 ft. = 48 / 12
48 X 1/4 = 12
48 + 12 + 60 bd. ft.

Or very simple with a small hand electronic calculator, the problem can easily be entered and figured thus:
Enter 6 X 1.25 X 8 X12 / 12 = 60 bd. ft.

In each case of the extra thickness, substitute the decimal equivalent in the formula:

5/4 = 1.25; 6/4 = 1.50; and 7/4 = 1.75. Of course, a 2-in. thickness is entered directly as 2.

Examples What is the price of 6 pieces of oak measuring 6/4 X 10 in. X 10 ft. long if the price per board foot is $1.95? (this is just hypothetical price)

Solution using the calculator:

Enter 6 X 1.5 X 10 X 10 / 12 = 75 bd. ft.
75 bd. ft X $1.95 = $146.25

Using just a pencil, the calculation would be:

6 X 1 X 10 X 10 / 12
600 / 12 = 50
50 X 1/2 = 25
50 + 25 = 75 bd. ft.

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