Quick answer

A board foot is 144 cubic inches of wood, the same as a board 1 inch thick, 12 inches wide, and 12 inches long. Formula: (Thickness in inches × Width in inches × Length in feet) ÷ 12.

BF = (T″ × W″ × L′) ÷ 12

What Is a Board Foot?

A board foot (BF) is a measure of volume. It is not a measure of length or surface area. One board foot equals 144 cubic inches, which matches a piece of wood 1 inch thick, 12 inches wide, and 12 inches long.

Any shape with the same volume also counts as 1 board foot. A board 2 inches thick, 6 inches wide, and 12 inches long is still 144 cubic inches, so it is also 1 BF.

Hardwood is usually sold by the board foot because boards arrive in random widths and lengths. Pricing by volume means you pay for the amount of wood you actually get. Dimensional softwood, such as framing 2×4s, comes in standard sizes, so stores often sell it by the piece or by the linear foot (a measure of length only).

The Board Foot Formula

The board foot formula has a few versions. They all give the same answer. Pick the one that matches the units on your tape measure.

Why divide by 12 in the first version? Length in feet is already 12 times smaller than length in inches. So 144 ÷ 12 leaves 12 as the divisor.

How to Calculate Board Feet (Step by Step)

Follow these seven steps for any board feet calculation. The working uses a 1″ × 6″ × 8 ft board as the example.

1. Measure thickness Measure the board’s thickness in inches. Use the thickness your supplier prices by, such as 1 inch for 4/4 rough lumber.
2. Measure width Measure the board’s width in inches.
3. Measure length Measure the board’s length in feet. If you measure in inches, keep the number in inches and use the ÷ 144 version of the formula.
4. Multiply the three dimensions Multiply thickness × width × length. For a 1″ × 6″ × 8 ft board, 1 × 6 × 8 = 48.
5. Divide Divide by 12 when length is in feet, or by 144 when all three dimensions are in inches. 48 ÷ 12 = 4 board feet.
6. Multiply by quantity Multiply the board feet per piece by the number of identical boards. 4 BF × 10 boards = 40 BF.
7. Add a waste allowance If you are buying material, add a waste allowance. With 10% extra, 40 BF × 1.10 = 44 BF to purchase.

Worked Examples

Each example shows the inputs, the full working, and the result. Results are rounded to two decimal places only at the end.

Understanding Lumber Thickness (Quarter Sizes)

Hardwood thickness is often written in quarters, meaning quarters of an inch. You may also hear this called “quarter sizes.” It is different from quartersawn, which describes how a log is cut. So 4/4 (said “four quarter”) means four quarters, or 1 inch.

Rough hardwood is usually priced by its rough, or nominal, thickness. A 4/4 board is billed as 1 inch thick even if it measures a little less after drying. Surfaced boards may be billed differently, so confirm the measurement basis with your supplier.

Nominal vs. Actual Lumber Sizes

The nominal size is the name of the board, like “2×4.” The actual size is what it measures after drying and planing. A surfaced softwood 2×4 is about 1.5″ × 3.5″, and a 1×6 is about 0.75″ × 5.5″.

Board Feet Quick-Reference Chart

This chart uses nominal dimensions (for example, 2″ × 4″ for a 2×4) and the formula (T × W × L) ÷ 12. Values are rounded to two decimal places.

Need actual sizes instead? Enter the measured dimensions into the formula. For example, an actual 1.5″ × 3.5″ × 8 ft board is (1.5 × 3.5 × 8) ÷ 12 = 3.5 BF.

How to Estimate Lumber Cost

Once you know the board feet, cost is simple multiplication. A waste allowance is extra material you buy to cover cutting loss, defects, and mistakes.

There is no universal waste figure. As general guidance only, many woodworkers start around 10–20% for clean, surfaced stock and plan more for rough lumber with knots or defects. Treat this as a purchasing allowance, not a guaranteed yield.

Common Board Foot Mistakes

• Mixing feet and inches. Keep thickness and width in inches, then use feet or inches for length consistently.
• Dividing by 12 when length is in inches. Inch-only measurements need ÷ 144. Dividing 1 × 6 × 96 by 12 gives 48, which is 12 times too high.
• Using the wrong size basis. Using actual size when your supplier prices by nominal size, or the reverse, will throw off your total.
• Forgetting quantity. Calculate one board, then multiply by the number of pieces.
• Skipping the waste allowance. Buying the exact volume often leaves you short after cutting.
• Confusing board feet with linear feet. A linear foot is length only; a board foot is volume.

Board Feet vs. Linear Feet vs. Cubic Feet

To convert board feet to cubic feet, divide by 12. For example, 48 BF ÷ 12 = 4 cubic feet.

Skip the Math: Try Our Free Board Foot Calculator

Enter your boards and get totals, waste, and cost instantly. Open the calculator

Frequently Asked Questions

What is a board foot?

A board foot is a unit of lumber volume equal to 144 cubic inches. That is the same amount of wood as a board 1 inch thick, 12 inches wide, and 12 inches long. Any board with the same volume, such as 2″ × 6″ × 12″, also equals 1 board foot.

How many board feet are in a 2×4×8?

Using nominal dimensions, a 2×4×8 is (2 × 4 × 8) ÷ 12 = 5.33 board feet. Using its actual surfaced size of about 1.5″ × 3.5″, it is (1.5 × 3.5 × 8) ÷ 12 = 3.5 board feet. Ask your supplier which basis they use, although 2×4s are usually sold per piece.

How do I calculate board feet in metric?

Convert each dimension to inches first. Divide millimeters by 25.4 or centimeters by 2.54. Then multiply thickness × width × length in inches and divide by 144. For example, 25.4 mm × 152.4 mm × 2438.4 mm becomes 1″ × 6″ × 96″, which equals 4 board feet.

Is a board foot the same as a linear foot?

No. A linear foot measures only length: 12 inches along the board, whatever its width or thickness. A board foot measures volume. A 1″ × 12″ board has 1 board foot per linear foot, but a 1″ × 6″ board has only 0.5 board feet per linear foot.

How many board feet are in a cubic foot?

One cubic foot contains 12 board feet. A cubic foot is 12″ × 12″ × 12″, or 1,728 cubic inches, and 1,728 ÷ 144 = 12. To convert board feet to cubic feet, divide by 12. To convert cubic feet to board feet, multiply by 12.

Why is hardwood sold by the board foot?

Hardwood boards often come in random widths and lengths, so pricing per piece or per linear foot would be unfair. Board feet price the actual volume of wood you buy, so a wide board costs more than a narrow one of the same length and thickness.

Should I use nominal or actual dimensions?

Use whichever dimensions your supplier uses for pricing. Rough hardwood is commonly measured by its rough thickness, such as 4/4 for 1 inch, while surfaced softwood has smaller actual sizes than its nominal name. Practices vary by region and supplier, so ask when you are unsure.

The Bottom Line

The board foot formula is simple: multiply thickness in inches by width in inches by length in feet, then divide by 12. Use ÷ 144 when every dimension is in inches, and convert metric to inches first. For multi-board projects with waste and cost, the free Board Foot Calculator does the work in seconds.

References

• National Hardwood Lumber Association: Rules for the Measurement and Inspection of Hardwood and Cypress
• American Hardwood Export Council: Measurement of sawn lumber
• American Wood Council: Weights and measurement