Board Foot Calculator: Formula and Examples

Calculate board feet by multiplying a board’s thickness in inches by its width in inches and length in feet, then dividing by 12. Enter those three measurements in the calculator to get the board’s nominal volume in board feet, a standard lumber-measurement unit.

Formula

Board feet = thickness (inches) × width (inches) × length (feet) ÷ 12. The divisor converts the dimensions to the volume represented by one board foot: a piece 1 inch thick, 12 inches wide, and 1 foot long.

• Thickness is the board’s thickness in inches.
• Width is its width in inches.
• Length is its length in feet.

The calculator also reports equivalent cubic feet. For dimensions entered in inches, that volume is thickness × width × length × 12 ÷ 1,728, which simplifies to thickness × width × length ÷ 144 when length is entered in feet. One cubic foot contains 12 board feet.

Worked Example

Using the calculator’s default dimensions—a board 1 inch thick, 6 inches wide, and 8 feet long:

1. Multiply thickness by width: 1 × 6 = 6 square inches.
2. Multiply by length: 6 × 8 = 48.
3. Divide by 12: 48 ÷ 12 = 4 board feet.
4. For cubic feet, calculate 1 × 6 × 8 ÷ 144 = 0.333…, which rounds to 0.333 ft³.

The displayed board-foot result is 4.00 bd ft when rounded to two decimal places; the equivalent volume is 0.333 ft³ when rounded to three.

What a Board Foot Measures

A board foot is a unit of lumber volume, not a measurement of a board’s surface area or its length. It describes the volume in a standard reference block measuring 1 inch × 12 inches × 12 inches. That block is 144 cubic inches, or one-twelfth of a cubic foot.

The unit is useful because lumber comes in many thicknesses and widths. A volume-based measure lets people compare or total pieces of different dimensions. For example, a board 2 inches thick, 6 inches wide, and 4 feet long also contains 4 board feet: 2 × 6 × 4 ÷ 12 = 4.

Board-foot calculations are common in lumber estimating and woodworking. They give a consistent way to state volume, but do not by themselves determine how much usable material a project will yield. Saw cuts, defects, drying, surfacing, and the shape of a project can affect usable output.

How to Measure and Convert Dimensions

Measure the thickness and width in inches, and the length in feet, then use the formula. If all three measurements are in inches, divide their product by 144 instead:

Board feet = thickness (in) × width (in) × length (in) ÷ 144.

If measurements are metric, convert to inches and feet first, or calculate the volume in cubic metres and convert it. One board foot equals 2,359.737216 cubic centimetres, approximately 0.00235974 m³. For dimensions in centimetres, multiply thickness × width × length, then divide by about 2,359.74 to obtain board feet. Keep the units consistent; applying the inches-and-feet formula directly to centimetres or metres gives an incorrect result.

For several pieces, calculate each board’s volume and add the results. If a group contains identical boards, calculate one board and multiply by the quantity. A calculator can make these repeated calculations quicker, but the measurements still need to reflect the lumber convention being used.

Nominal Versus Actual Lumber Size

A frequent source of disagreement is whether the calculation uses a board’s nominal size or its actual measured size. Nominal dimensions are the named or rough size; surfaced lumber is often smaller after drying and planing. For example, lumber commonly called “2 × 4” typically measures about 1½ × 3½ inches after surfacing, though dimensions can vary by product and region.

Using the nominal 2 × 4 dimensions produces a different board-foot figure from using 1½ × 3½. Neither calculation is automatically the right one for every purpose: use the dimensions specified by the lumber seller, grading convention, estimate, or project. For a physical volume estimate, actual dimensions are generally the relevant measurements; for a purchase or lumber tally, the applicable sales convention may use nominal dimensions.

Board-foot conventions can also vary for rough, surfaced, or figured lumber. Check how the dimensions are defined before comparing quoted quantities. A calculator applies the arithmetic only; it cannot decide which convention applies to a particular transaction.

Common Calculation Mistakes

• Mixing units: The standard formula expects inches for thickness and width, and feet for length. Convert before calculating.
• Forgetting the divisor: Divide by 12 when length is in feet, or by 144 when all dimensions are in inches.
• Confusing board feet with square feet: Board feet measure volume; square feet measure area.
• Rounding too early: Keep full precision while adding multiple pieces, then round the final total to a useful level.
• Ignoring the size convention: Nominal and actual dimensions can differ, so state which you used.

The calculation assumes a rectangular piece with uniform dimensions. Irregular or tapered stock may require a more detailed volume estimate. A numerical result also does not account for knots, cracks, kerf (material removed by a saw), or other waste.

Frequently Asked Questions

How many board feet are in a 2 × 4 × 8?
Using nominal dimensions in inches and feet, the result is 2 × 4 × 8 ÷ 12 = 5⅓ board feet. If the board’s actual surfaced dimensions are about 1½ × 3½ inches, the physical-volume calculation is 3½ board feet.

How do I calculate board feet in a log?
A log is not a rectangular board, so the board formula does not directly give its usable lumber yield. Log-scale rules estimate potential lumber volume from measurements such as diameter and length; results depend on the scaling rule and assumptions about sawing and waste.

How many board feet are in a cubic foot?
There are 12 board feet in one cubic foot. One board foot is 1/12 of a cubic foot, or 144 cubic inches.

Do I use nominal or actual dimensions?
Use the dimensions required for the purpose. Actual dimensions suit a physical-volume calculation, while a lumber tally or quotation may follow a stated nominal or trade convention. Confirm the convention rather than assuming the two are interchangeable.

Can I add board feet from different-sized boards?
Yes. Calculate each piece using a consistent measurement convention and add the results. For identical boards, multiply the board-foot amount for one by the number of boards.

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in thickness | Thickness | in | 1 | 0
in width | Width | in | 6 | 0
in length | Length | ft | 8 | 0
out boardfeet | Board feet | bd ft | thickness * width * length / 12 | 2
out cubicfeet | Equivalent volume | ft³ | thickness * width * length / 144 | 3