How to Calculate Board Feet

Board feet measure lumber volume, so the calculation accounts for thickness, width, and length. It is especially useful when buying hardwood, rough-sawn boards, slabs, or other stock sold by volume. Once the units are consistent, the math is straightforward.

Board Foot Formula

For dimensions commonly shown on a lumber list, use this board foot formula:

For multiple identical boards, include the quantity:

If all three dimensions are in inches, divide by 144 instead. Both versions work because one board foot equals 144 cubic inches.

How to Calculate Board Feet Step by Step

1. Measure thickness and width in inches. Use the board's actual dimensions when you need its true volume.
2. Measure length in feet. Convert any remaining inches to a fraction of a foot. For example, 6 inches is 0.5 foot.
3. Multiply the three dimensions. Thickness × width × length gives the volume before the board-foot conversion.
4. Divide by 12. The result is the board feet in one piece.
5. Multiply by quantity. Do this only for boards with the same dimensions. Calculate different sizes separately, then add their totals.

For a quicker total, enter each size in the free board foot calculator. It can combine multiple board sizes and add a waste allowance.

Worked Board Feet Examples

Example 1: One board

Find the volume of a board that measures 1 inch thick, 8 inches wide, and 10 feet long:

1 × 8 × 10 ÷ 12 = 6.67 board feet

Example 2: Several identical boards

You need six boards, each 2 inches thick, 6 inches wide, and 8 feet long:

2 × 6 × 8 × 6 ÷ 12 = 48 board feet

This board feet example includes quantity in a single calculation. You could also find the 8 board feet in one board and multiply by six.

Example 3: A length with feet and inches

A board is 1.5 inches thick, 9 inches wide, and 6 feet 6 inches long. Convert 6 inches to 0.5 foot, making the length 6.5 feet:

1.5 × 9 × 6.5 ÷ 12 = 7.31 board feet

Example 4: Using actual dimensions

An 8-foot board sold as a nominal 2×4 commonly has finished dimensions of 1.5 by 3.5 inches. Using those actual measurements:

1.5 × 3.5 × 8 ÷ 12 = 3.5 board feet

Using the nominal 2 by 4 dimensions would produce 5.33 board feet. That difference is why you should confirm which dimensions the lumber seller uses.

How to Calculate Board Feet for Lumber Purchases

Start with a cut list grouped by thickness, width, and length. Calculate each group separately and add the results. Then account for material lost to saw kerfs, defects, end trimming, milling, and grain matching. The right allowance depends on the stock and project, so base it on the boards you are buying and the cuts you plan to make rather than treating one percentage as universal.

To estimate cost, multiply the purchase quantity in board feet by the supplier's price per board foot. Confirm whether the supplier measures rough or surfaced dimensions and how they round a tally before comparing quotes.

Common Board Foot Calculation Mistakes

• Mixing feet and inches. The divide-by-12 formula expects thickness and width in inches but length in feet.
• Using nominal dimensions unintentionally. A size name such as 2×4 may not match the board's measured size.
• Forgetting quantity. The basic formula calculates one board unless quantity is included.
• Combining unlike boards too early. Calculate each distinct size first, then add the board-foot totals.
• Rounding every line too soon. Keep extra decimal places until the final total to avoid accumulated rounding error.
• Confusing board feet with linear feet. Linear feet measure length; board feet measure volume.
• Treating the calculated volume as the complete purchase plan. Cuts, defects, and milling can require additional material.

Frequently Asked Questions