The Board Foot Formula

The Standard Industry Equation

Whether you are a professional contractor or a hobbyist woodworker, mastering the board foot formula is the first step toward accurate project budgeting. Because wood is a three-dimensional product, we cannot rely on linear measurements alone. The board foot formula accounts for thickness, width, and depth in one unified number.

Step-by-Step Calculation Logic

To ensure you never make a mistake at the lumber yard, apply this 5-step process to every board you measure:

• Step 1: Measure thickness (T) in inches. (e.g., 2 inches)
• Step 2: Measure width (W) in inches. (e.g., 6 inches)
• Step 3: Measure length (L) in feet. (e.g., 8 feet)
• Step 4: Multiply T × W × L. (2 × 6 × 8 = 96)
• Step 5: Divide the total by 12. (96 / 12 = 8 Board Feet)

Working with Length in Inches

Sometimes, especially for smaller furniture parts, your length will be measured in inches rather than feet. In this case, the formula changes slightly. Instead of dividing by 12, you must divide the total cubic inches by 144.

Formula: (T" × W" × L") / 144

Example: A small piece of cherry is 1" thick, 4" wide, and 12" long. (1 × 4 × 12) / 144 = 0.33 Board Feet.

Common Lumber Size Chart

Don't Forget the Waste Factor

The formula gives you the Net Board Feet. However, wood is a natural product and often contains knots, sapwood, or cracks that must be cut out. Professional lumber orders always multiply the net BF by a factor of 1.15 or 1.20 to ensure they have enough usable material.