Q & A: Board Feet Calculation

Q:

I used to buy planed and jointed lumber (S4S) at a home center where it was sold by the lineal foot.Now that I have a planer and jointer, I want to buy my lumber in the rough but I’m confused. It’s sold by the “board foot.” What does board foot (bd. ft.) really mean and how do I calculate it?

A:

Lineal feet is a measure of length.
Board feet is a measure of volume. In
the same way that sand is sold by the
cubic yard, rough lumber is sold by the
board foot.

Calculating board feet for 4/4 (1-in.
thick) lumber is easy. Simply figure out
the board’s surface measure:

Full width in inches times length in
feet divided by 12.

“Full width” is rounded up or down
to the nearest whole inch. “Length in
feet” is a whole number, too. Board feet
are rounded to the nearest whole foot.

To calculate the number of board
feet in a thicker board, multiply the
surface measure by the thickness of
the board.Here’s an example for a 6/4
(1-1/2-in. thick) board that’s 7-3/8-in.
wide and 8 ft. 3-in. long:

Board feet = (W x L x TH)/12
                  = (7 x 8 x 1-1/2)/12

                  = 7 board feet

For your calculations, be sure to
ask your lumber supplier if their
3/4-in. planed boards are considered
1-in. thick. Some are, some aren’t.

Click any image to view a larger version.

One board foot is 1-in. thick x
12-in. wide x 12-in. long.

This story originally appeared in American Woodworker October 2000, issue #82.

October 2000, issue #82

Purchase this back issue.