A board foot (bf) is a lumber volume measurement used in North America. One board foot equals 12 cubic inches. Board feet volume is calculated by multiplying the nominal width by the nominal thickness by the actual length of the boards. You can convert board feet to a per lineal foot amount based on the thickness and width of the lumber. To get one board foot in 1 x 2's, you will need six lineal feet of 1 x 2's. For 1 x 12's, you will need one lineal foot of 1 x 12.
A lineal foot (Lf) is 12 inches long. Twenty feet is the same as 20 lineal feet, and no conversion is needed between the two.
Lf = 12/(T*W)*bf
where Lf is lineal feet bf is the board foot amount T the nominal thickness of the board W the nominal width of the board
Convert 600 board feet of 1 x 2 lumber to a lineal foot amount;
Lf = 12 ÷ (1 * 2) * 600 12 ÷ 2 * 600 = 600 6 * 600 =3600
600 board feet of 1 x 2 lumber makes 3600 lineal feet of 1 x 2's