How to Calculate Board Feet (Formula and Examples)

Short answer: board feet = thickness (in) × width (in) × length (ft) ÷ 12. One board foot is 144 cubic inches, the same as a board 1 inch thick, 12 inches wide and 1 foot long. A 2 × 6 that’s 10 ft long is 2 × 6 × 10 ÷ 12 = 10 board feet.

For a whole stack of boards and the total cost, use the board foot calculator.

Three ways to write the formula

• Length in feet: T (in) × W (in) × L (ft) ÷ 12
• Length in inches: T (in) × W (in) × L (in) ÷ 144
• All in feet: T (ft) × W (ft) × L (ft) × 12

They all give the same answer. Use whichever matches how you measured.

Worked examples

1. A 1 × 6 board, 8 ft long: 1 × 6 × 8 ÷ 12 = 4 board feet.
2. A 2 × 4 stud, 8 ft long: 2 × 4 × 8 ÷ 12 = 5.33 board feet.
3. Five 8/4 walnut boards, 8 in wide and 10 ft long: 2 × 8 × 10 ÷ 12 = 13.33 each, × 5 = 66.67 board feet.
4. A board 1 in thick, 9 in wide and 96 in long: 1 × 9 × 96 ÷ 144 = 6 board feet.

Board feet per foot of length

Size	Board feet per foot	8 ft board	12 ft board
1 × 4	0.33	2.67	4
1 × 6	0.50	4	6
1 × 8	0.67	5.33	8
2 × 4	0.67	5.33	8
2 × 6	1.00	8	12
2 × 8	1.33	10.67	16
2 × 10	1.67	13.33	20
2 × 12	2.00	16	24
4 × 4	1.33	10.67	16

Quarters and nominal sizes

• Hardwood thickness in quarters: 4/4 = 1 in, 5/4 = 1¼ in, 6/4 = 1½ in, 8/4 = 2 in. Hardwood is priced by this rough-sawn thickness, even after it is planed thinner.
• Construction lumber: a 2 × 4 actually measures about 1½ × 3½ in, but yards price board feet on the name (nominal) size. Use 2 × 4 in the formula.

Common questions

How many board feet are in a cubic foot?

12. A cubic foot is 1,728 cubic inches, and a board foot is 144.

Do I include waste?

Board feet measure what you buy. When planning a project, add 15 to 30% for defects, cuts and offcuts, depending on the wood and how fussy the project is.

How do I price lumber by the board foot?

Multiply the board feet by the price per board foot. 66.67 board feet at $9.50 is $633.33.