Board Foot Calculator

How do you calculate board feet?

A board foot calculator measures lumber by volume: board feet = thickness in inches × width in inches × length in feet ÷ 12, multiplied by the number of boards. Ten 2×6 boards that are 8 ft long hold 80 board feet, which costs $320 at $4 per board foot. The calculator shows the total, the cost, and the board feet in a single board.

Board feet let a lumber yard price a stack of random-width hardwood fairly. One customer takes three wide boards, another takes six narrow ones, and both pay for the wood they actually carry out.

The formula in plain words

1. Multiply thickness × width, both in inches. This is the end-grain area in square inches.
2. Multiply by the length in feet.
3. Divide by 12 to get board feet for one board.
4. Multiply by the number of boards, then by the price per board foot.

The divide-by-12 step comes from the definition: 1 in × 12 in × 1 ft is exactly one board foot.

Worked examples

Ten 2×6 boards, 8 ft long, $4 per board foot

• One board: 2 × 6 × 8 ÷ 12 = 8.00 BF
• Ten boards: 8 × 10 = 80.00 BF
• Cost: 80 × $4 = $320.00

Six walnut boards for a table top: 4/4 (1 in) thick, 7 in wide, 9 ft long, $9.50 per board foot

• One board: 1 × 7 × 9 ÷ 12 = 5.25 BF
• Six boards: 5.25 × 6 = 31.50 BF
• Cost: 31.5 × $9.50 = $299.25

Plan on extra for defects and milling. Furniture makers often buy 20–30% more rough lumber than the finished parts need, since knots, checks, and planing all eat into the boards.

Board feet by size and length

Nominal size	BF per linear ft	8 ft	12 ft	16 ft
1 × 4	0.33	2.67	4.00	5.33
1 × 6	0.50	4.00	6.00	8.00
1 × 8	0.67	5.33	8.00	10.67
2 × 4	0.67	5.33	8.00	10.67
2 × 6	1.00	8.00	12.00	16.00
2 × 8	1.33	10.67	16.00	21.33
2 × 10	1.67	13.33	20.00	26.67
2 × 12	2.00	16.00	24.00	32.00
4 × 4	1.33	10.67	16.00	21.33
6 × 6	3.00	24.00	36.00	48.00

These use nominal sizes, which is how board feet are normally counted for dimension lumber. A 2×4 actually measures about 1½ × 3½ in, but it is still billed as 2 × 4.

Hardwood thickness in quarters

Quarter size	Rough thickness	Typical surfaced thickness
4/4	1 in	about ¾–13/16 in
5/4	1¼ in	about 1–1 1/16 in
6/4	1½ in	about 1¼–1 5/16 in
8/4	2 in	about 1¾ in

Enter the rough thickness to match how most hardwood dealers bill.

How to measure a board

• Measure width at the narrowest usable point on a rough board with waney edges.
• Measure length in feet, rounding down to the nearest usable half foot.
• Use the quarter size for thickness, not a tape reading of the planed board.
• Group identical boards and enter the count instead of running each one.

Common mistakes

• Mixing inches and feet. Entering length in inches makes the answer 12 times too big.
• Comparing per-piece and per-BF prices directly. A $12 board that holds 8 BF costs $1.50 per board foot. Convert before you compare.
• Forgetting the waste factor. Board feet measure what you buy, not what ends up in the finished project.
• Ignoring weight. A truckload of green oak is heavy. The lumber weight calculator turns board feet into pounds.

For framing jobs priced by the piece, the stud calculator and framing calculator count pieces instead. Sheet goods belong in the plywood calculator.