About Board Foot Calculator (Lumber BF & Cost)
The board foot calculator converts a lumber list into board feet (BF), the standard volume unit lumber is bought and sold by: one board foot is a piece 1 inch thick by 12 inches wide by 1 foot long, so BF = thickness (in) x width (in) x length (ft) / 12. By trade convention board feet always use NOMINAL dimensions — a 2x6 counts as 2 by 6 even though it actually dresses to 1.5 by 5.5 inches — and this tool follows that convention throughout.
Enter each item as nominal thickness, nominal width, length in feet, and a piece count; hardwood buyers can pick the quarters thickness (4/4, 5/4, 6/4, or 8/4) from the shortcut instead of typing inches. Add an optional price in dollars per board foot on any line to get its cost, and the tool sums total board feet, the board feet that carry a price, and the total cost across the list. A reference table shows the actual dressed size behind each nominal dimension — for display only, since the BF math always stays nominal.
How It Works
- Add one line per lumber size: nominal thickness (in), nominal width (in), length (ft), and how many identical pieces. Use the quarters shortcut to fill hardwood thicknesses: 4/4 = 1 in, 5/4 = 1.25 in, 6/4 = 1.5 in, 8/4 = 2 in.
- Each line computes BF per piece as thickness x width x length / 12 using the NOMINAL dimensions (trade convention — never the dressed actual size), then multiplies by the piece count for the line total.
- Optionally enter a price in $ per board foot on any line; the line cost is its total BF times that price. Lines without a price are excluded from the cost math.
- The totals card sums board feet over every line, shows the priced BF subtotal, and totals the cost across priced lines only (no cost is shown when nothing is priced).
- Check the nominal-vs-actual reference table when planning finished dimensions: a nominal 1 in board dresses to 3/4 in and a nominal 6 in width dresses to 5-1/2 in, but both still count at their nominal size for board feet.
Worked Example
A furniture maker prices ten 2x6 boards, 8 feet long, quoted at $0.85 per board foot. Each board is 2 x 6 x 8 / 12 = 8 board feet — using the nominal 2 by 6, not the 1.5 by 5.5 actual dressed size. Ten boards make 8 x 10 = 80 BF, and at $0.85/BF the line costs 80 x 0.85 = $68.00. Adding an unpriced 5/4 x 6 hardwood board 10 ft long (1.25 x 6 x 10 / 12 = 6.25 BF) and an unpriced 1x4 6 ft long (1 x 4 x 6 / 12 = 2 BF) brings the list to 88.25 BF total, with the priced subtotal still 80 BF and the total cost still $68.00.
Formulas
- Board feet per piece
BF_each = T_nom x W_nom x L / 12- Line and list totals
BF_line = BF_each x n; BF_total = sum(BF_line)- Cost (priced lines only)
Cost_line = BF_line x price; Cost_total = sum over priced lines- Hardwood quarters thickness
T_nom = quarters / 4 (4/4 = 1 in, 5/4 = 1.25 in, 6/4 = 1.5 in, 8/4 = 2 in)
Standards & References
- Lumber trade convention -- board feet from NOMINAL dimensions
- American Softwood Lumber Standard PS 20 -- nominal vs dressed sizes
- NHLA hardwood convention -- thickness sold by quarters (4/4, 5/4, 6/4, 8/4)
Frequently Asked Questions
Do board feet use nominal or actual lumber dimensions?
Always nominal — that is the lumber trade convention this calculator follows. A 2x6 actually measures 1.5 x 5.5 inches after drying and surfacing, but it still counts as 2 x 6 for board feet: an 8-ft 2x6 is 2 x 6 x 8 / 12 = 8 BF, not the 5.5 BF its actual dimensions would give. Sawmills price rough lumber by the volume it was cut at, and the whole supply chain quotes BF on the same nominal basis, so mixing in actual sizes would misprice every quote.
What exactly is one board foot?
One board foot is the volume of a board 1 inch thick, 12 inches wide, and 1 foot long — 144 cubic inches of nominal lumber volume. The working formula is thickness (in) x width (in) x length (ft) / 12. It is a volume unit, not a length: a 12-ft 1x12 and a 6-ft 2x12 are both exactly 12 board feet.
What does 4/4, 5/4, 6/4, or 8/4 hardwood mean?
Hardwood thickness is quoted in quarters of an inch of rough-sawn thickness: 4/4 ("four-quarter") is 1 inch, 5/4 is 1.25 in, 6/4 is 1.5 in, and 8/4 is 2 in. Board feet for hardwood use that quarters thickness as the nominal dimension, so a 5/4 x 6 board 10 ft long is 1.25 x 6 x 10 / 12 = 6.25 BF. After surfacing, 4/4 stock typically finishes near 13/16 in, which is why you buy thicker quarters than your finished part needs.
How do I estimate lumber cost from a $/BF price?
Multiply the line’s total board feet by the quoted price per board foot: ten 8-ft 2x6 boards are 80 BF, and at $0.85/BF they cost 80 x 0.85 = $68.00. This calculator takes an optional price on each line, totals cost across the priced lines only, and reports the priced-BF subtotal so you can see how much of the list the cost figure actually covers.
Is a linear foot the same as a board foot?
No. A linear (lineal) foot measures only length along the board and ignores the cross-section, while a board foot measures volume. One linear foot of 1x12 is 1 BF, but one linear foot of 2x4 is only 0.667 BF. To convert, multiply linear feet by the nominal thickness times nominal width divided by 12 for that specific size.
Should I add a waste factor to my board-foot takeoff?
Yes, for real projects. Board feet measure what you buy, not what ends up in the finished piece: defects, checking, planing, jointing, and cutoffs all consume material. Furniture makers commonly add 15 to 30 percent over the net board feet of the cut list, and more for highly figured or narrow-width stock. This tool reports the net BF of the list you enter — apply your waste factor to the piece counts or the total before ordering.