How to Calculate Board Feet

Multiply thickness (in) by width (in) by length (ft), then divide by 12. That is the whole method. Below are the steps, worked examples and the mistakes to avoid. Want the answer now? Use the board feet calculator.

What is the formula for board feet?

Board feet equal thickness in inches times width in inches times length in feet, divided by 12. If the length is in inches, divide by 144 instead. One board foot is a piece 1 inch thick, 12 inches wide and 12 inches long, which holds 144 cubic inches of wood.

BF = T (in) × W (in) × L (ft) ÷ 12
BF = T (in) × W (in) × L (in) ÷ 144

Ohio State University Extension, Penn State Extension and the University of Wisconsin Extension all use this definition and formula [1] [2] [3].

Step by step

1. Measure the thickness in inches. Use the nominal size the seller uses, such as 4/4 for 1 inch hardwood or 2 for a 2x4.
2. Measure the width in inches. For a board that tapers, measure one third of the way from the narrow end.
3. Measure the length in feet. If you measured in inches, divide by 12 to get feet.
4. Multiply and divide by 12. Thickness × width × length in feet ÷ 12 gives board feet for one piece.
5. Multiply by the number of pieces. Add the totals for each size to get the board feet for the whole order.

The rule for tapered boards comes from the hardwood grading rules described by the University of Washington [4].

Worked examples

A 4/4 cherry board

The board is 1 inch thick, 7 inches wide and 9 feet long. 1 × 7 × 9 ÷ 12 = 5.25 board feet.

Ten 2x4s, 8 feet long

One 2x4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet. Ten of them are 53.33 board feet.

An 8/4 walnut slab

The slab is 2 inches thick and 66 inches long. Its width is 14, 17 and 20 inches at three points, so the average is 17 inches. 2 × 17 × 66 ÷ 144 = 15.58 board feet.

A stack of lumber

A stack is 36 inches high, 60 inches wide and made of 8 foot boards. 36 × 60 × 8 ÷ 12 = 1,440 board feet. This example is from the University of Wisconsin Extension [3]. Gaps between boards make the real number lower.

How do hardwood graders figure board feet?

Hardwood graders first find the surface measure: width in inches times length in feet, divided by 12, rounded to a whole number. Then they multiply the surface measure by the nominal thickness in inches. A 2 inch board, 6 1/4 inches wide and 8 feet long, has a surface measure of 4 and holds 8 board feet.

That example and method come from AHEC [5]. The University of Washington adds that boards thinner than 1 inch are counted as 1 inch, and any fraction of a foot in length is dropped [4]. So a hardwood yard tally can differ a little from the plain formula.

Board feet from metric sizes

Multiply thickness, width and length in meters to get cubic meters. Divide by 0.002359737216 to get board feet. That number comes from 144 cubic inches and the exact inch of 0.0254 meters set by NIST [6].

Common mistakes

• Mixing units. Use inches for thickness and width, and feet for length, or divide by 144 if all are inches.
• Using planed sizes when the seller tallies nominal sizes. Ask which one they use.
• Forgetting the piece count, or adding waste twice.
• Using the board formula on a round log. Logs need a log rule.

Questions

References

1. Measuring Standing Trees (F-35-02). Ohio State University Extension.
2. Forest Stewardship: Terminology. Penn State Extension.
3. What Is a Board Foot? Forestry Facts No. 42. University of Wisconsin Extension.
4. Briggs, D. Forest Products Measurements and Conversion Factors, Chapter 4, Lumber. University of Washington, Rural Technology Initiative.
5. Grading Sawn Lumber: Measurement. American Hardwood Export Council.
6. NIST Special Publication 811, Appendix B.9, Conversion Factors. National Institute of Standards and Technology.

Written and checked by the editors of Board Foot Calculator. Every formula on this page is tested with sample values from the sources above. How we work. Last updated: October 20, 2026.