Board Foot (BF)

A board foot is the standard US unit of lumber volume: a piece 1 inch thick, 12 inches wide and 12 inches long, or 144 cubic inches. Lumber yards use it to price hardwood, quote framing packages and compare boards of different sizes on equal terms.

The formula

Board feet = Thickness (in) × Width (in) × Length (ft) ÷ 12

If every dimension is in inches, divide by 144 instead:

Board feet = Thickness (in) × Width (in) × Length (in) ÷ 144

Nominal, not actual, size

Softwood dimensional lumber is graded and sold by its nominal size under the American Softwood Lumber Standard (PS 20). A 2x6 actually measures 1-1/2” × 5-1/2” after drying and planing, but it is still figured as 2” × 6” when counting board feet. That is why a 2x6 is always exactly 1 BF per linear foot, even though its real cross-section is only about 69% of that.

Hardwood: the quarter system

Hardwood is sold rough-sawn by thickness in quarters of an inch: 4/4 (“four-quarter”) is 1”, 5/4 is 1-1/4”, 8/4 is 2”. Board feet are calculated from that rough thickness and the board’s actual width and length, because hardwood boards come in random widths. A 4/4 board 7” wide and 10’ long is 1 × 7 × 10 ÷ 12 = 5.83 BF. Budget 20–30% extra for defects and the material lost to surfacing.

Board feet vs. linear feet

Linear feet measure length only. Board feet measure volume. Trim, molding and decking are usually priced per linear foot; hardwood and timber packages per board foot. Framing lumber at big-box stores is priced per piece, but contractor yards quote it per MBF (1,000 board feet) — divide the MBF price by 1,000 to get dollars per board foot.

Common mistakes

• Using actual dimensions for softwood. You’ll undercount by roughly 25–30% and won’t match the yard’s invoice.
• Mixing feet and inches. Use “÷ 12” only when length is in feet.
• Forgetting waste. Add 10–15% for crooked boards, knots and cut-offs on framing; more for hardwood furniture work.