Board Foot Calculator

What a board foot is and how to use the calculator

A board foot is a volume: a piece 1 inch thick, 12 inches wide and 1 foot long, or 144 cubic inches. In the United States both softwood and hardwood lumber are tallied in board feet, so boards of different sizes can be priced by the amount of wood they contain.

1. Choose inches and feet, or millimeters and meters.
2. In inches, say whether you are entering nominal sizes (what the lumber is called, such as 2×4) or actual sizes you measured.
3. Enter one row per size: the number of pieces, thickness, width and length. Add rows for a whole list.
4. Add a price per board foot (or per cubic meter) to estimate the cost.

With nominal sizes the calculator also shows how much wood you actually get, using the standard dressed sizes. For concrete, gravel or other bulk materials, see the concrete calculator; to convert between volume units, use the volume converter.

Board foot formula

T, W

thickness and width in inches

L

length in feet

n

number of pieces

t, w, l

thickness and width in millimeters, length in meters

Dividing by 12 turns inches × inches × feet into board feet: 1 × 12 × 1 ÷ 12 = 1. One board foot is 144 cubic inches, which is exactly 0.002359737216 m³ because an inch is exactly 25.4 mm; a cubic meter is about 423.78 board feet and a cubic foot is 12 board feet.

Worked example

The starting list: ten 2×4s, 8 ft long, and four 1×6 boards, 10 ft long, entered by nominal size.

1. 2×4s: 10 × 2 × 4 × 8 ÷ 12 = 53.33 BF
2. 1×6s: 4 × 1 × 6 × 10 ÷ 12 = 20 BF
3. Total: 73.33 board feet, which is 6.111 ft³ or 0.173 m³ at nominal size

At $1.25 per board foot that is 73.33 × $1.25 = $91.67. The dry dressed pieces are smaller: 10 × 1½ × 3½ × 8 ÷ 12 = 35 BF plus 4 × ¾ × 5½ × 10 ÷ 12 = 13.75 BF, so the wood you take home is 48.75 board feet (0.115 m³).

A hardwood example: one 8/4 board 7 in wide and 10 ft long is 2 × 7 × 10 ÷ 12 = 11.67 board feet. In metric, ten pieces of 38 × 89 mm at 2.4 m plus four of 19 × 140 mm at 3 m are 0.1131 m³, or 47.92 board feet.

Nominal and actual lumber sizes

Softwood lumber is named by nominal size. Under the American Softwood Lumber Standard (PS 20, published by NIST), the nominal size is a label, larger than the dressed size: a dry 2 by 4 is surfaced to 1½ × 3½ inches (38.1 × 88.9 mm). The standard defines board measure using nominal thickness and width, so the board feet on a softwood invoice are counted from the nominal size. It also says invoices for dressed lumber should show the actual thickness and width, and that cubic measure uses the dressed sizes.

“Dry” in PS 20 means a moisture content of 19% or less; green lumber is dressed slightly larger. The calculator uses the dry sizes and covers boards and dimension lumber up to 4½ in nominal thickness, not timbers.

Limits and tips

• Hardwood is usually sold in random widths and lengths; a yard may measure each board and round its surface area, so its tally can differ slightly from the exact figure here.
• The cost is the lumber only. Add extra for offcuts and defects when you order — how much depends on the grade and your cutting list.
• The dressed sizes are PS 20 minimums for dry softwood. Some mills and species (for example rough-sawn or green lumber) run larger.
• For flooring, decking or roofing sold by area, the square footage calculator and roofing calculator are a better fit.