Board Foot Conversion Calculator & Formula

This board foot conversion calculator converts any lumber measurement—thickness, width, and length—into board feet, the standard unit for buying and selling hardwood in North America. You enter the dimensions in inches and feet, and it returns the board foot volume, plus the equivalent in cubic feet and cubic meters for comparison. One board foot equals a piece 12 inches wide, 12 inches long, and 1 inch thick (144 cubic inches).

Formula

The standard board foot formula is:

Board Feet = (Thickness (in) × Width (in) × Length (ft)) / 12

Where:

• Thickness is in inches (in)
• Width is in inches (in)
• Length is in feet (ft)
• 12 is the conversion factor (12 inches per foot, and the 1-inch thickness basis)

If you measure length in inches instead, use: Board Feet = (Thickness × Width × Length in inches) / 144.

Worked Example

Using the default values: thickness = 1 in, width = 6 in, length = 8 ft.

1. Multiply thickness × width × length: 1 × 6 × 8 = 48
2. Divide by 12: 48 / 12 = 4.00 board feet

The calculator shows 4.00 bd ft. For cubic feet: (1 × 6 × 96) / 1728 = 0.333 cu ft. For cubic meters: (1 × 6 × 96) / 61023.744 ≈ 0.009 m³.

Why Use Board Feet?

Board feet is the universal pricing unit for rough-sawn hardwood lumber in the US and Canada. Unlike softwood (which is sold by nominal dimensions like 2×4), hardwood is sold by actual volume. A 1-inch thick, 6-inch wide, 8-foot long board is 4 board feet. If the same board were 2 inches thick, it would be 8 board feet. This system lets buyers compare prices across different thicknesses and widths directly: a price of $5 per board foot is the same regardless of whether the board is 4/4 or 8/4 thickness.

How to Measure Lumber for Board Feet

To get accurate results, you need to measure the actual dimensions of the wood, not the nominal ones. For example, a “2×4” actually measures 1.5 × 3.5 inches. Use a tape measure or calipers for thickness and width. Length is usually measured in feet, but if you have inches, convert by dividing by 12. Always measure the rough dimensions before planing or surfacing—lumber is often sold rough and then milled to final size.

Common Mistakes and Misconceptions

• Using nominal instead of actual size: A 2×4 is not 2×4 inches. Using nominal dimensions overestimates board feet by about 30%.
• Forgetting to divide by 12: The formula includes a division by 12 because thickness and width are in inches while length is in feet. If you mix units, you get a wrong number.
• Confusing board feet with square feet: Board feet measure volume, not area. A 1-inch thick board that is 1 square foot is 1 board foot; a 2-inch thick board of the same area is 2 board feet.
• Rounding too early: Round only the final result, not intermediate steps, to avoid cumulative error.

Limits of the Formula

The board foot formula assumes a perfect rectangular prism. It does not account for taper, wane, or defects. In real lumber, you often pay for the full volume including waste, and the usable yield is less. For logs, the formula is different (using log rules like Doyle or Scribner). This calculator is for cut lumber, not logs. Also, board foot pricing typically applies to rough lumber; if you buy surfaced (S4S) lumber, the dimensions are smaller but the price is still based on the rough size.

Frequently Asked Questions

How many board feet are in a 2x4x8?

A standard 2x4x8 (nominal) actually measures 1.5 × 3.5 × 96 inches. Using the formula: (1.5 × 3.5 × 8) / 12 = 3.5 board feet. If you used nominal 2×4×8, you’d get 5.33 bd ft, which is incorrect.

What is the difference between board foot and linear foot?

A linear foot is simply a length of 12 inches, regardless of width or thickness. A board foot is a volume unit: 144 cubic inches. For example, a 1×6 board that is 8 feet long has 4 board feet but 8 linear feet. Linear foot is used for moulding, trim, and other materials sold by length.

How do I convert board feet to cubic feet?

One board foot equals 1/12 of a cubic foot (since 144 cubic inches ÷ 1728 cubic inches per cubic foot = 0.08333). So multiply board feet by 0.08333 to get cubic feet. Conversely, multiply cubic feet by 12 to get board feet.

Why is hardwood sold by board foot but softwood by linear foot?

Hardwood is typically sold rough in random widths and lengths, so volume pricing makes sense. Softwood (like dimensional lumber) is milled to standard sizes and sold by length, so linear foot pricing is simpler. This is a historical convention, not a mathematical necessity.

Does the formula work for metric measurements?

No, the formula is designed for inches and feet. For metric, you can convert to inches first (1 inch = 25.4 mm) or use the cubic meter equivalent. One board foot equals 0.00235974 cubic meters. Our calculator includes a cubic meters output for convenience.

What does “4/4” mean in lumber?

It’s a fractional thickness notation: 4/4 = 1 inch, 6/4 = 1.5 inches, 8/4 = 2 inches. The numerator is quarters of an inch. When you see “4/4 oak,” it means 1-inch thick oak. This notation is common in hardwood grading.

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in t | Thickness | in | 1 | 0
in w | Width | in | 6 | 0
in l | Length | ft | 8 | 0
out bf | Board feet | bd ft | (t * w * l) / 12 | 2
out cf | Cubic feet | cu ft | (t * w * (l * 12)) / 1728 | 2
out cm | Cubic meters | m³ | (t * w * (l * 12)) / 61023.744 | 3