What Is a Board Foot?
When you step into a lumberyard to buy hardwood for a project, you'll find that it's often sold by the "board foot." This can be confusing for those accustomed to buying dimensional lumber (like 2x4s) by the piece or linear foot. A board foot is a unit of volume, not length. It represents a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick. This unit of measure is the industry standard for hardwoods because it provides a consistent way to price lumber of varying thicknesses and widths. A board foot calculator is an indispensable tool for any woodworker to accurately determine the volume of wood they need and to budget for their project costs.
The Board Foot Formula
The formula for calculating board feet is simple and relies on the three dimensions of a piece of lumber:
- Thickness: The thickness of the board, measured in inches. For rough-sawn lumber, this is often expressed in quarters (e.g., 4/4 for a 1-inch board, 8/4 for a 2-inch board).
- Width: The width of the board, also measured in inches.
- Length: The length of the board, measured in feet.
For example, a board that is 2 inches thick, 6 inches wide, and 8 feet long contains `(2 × 6 × 8) / 12 = 8` board feet. Our calculator takes this a step further by allowing you to input the quantity of boards and the cost per board foot to provide a total volume and estimated cost.
Nominal vs. Actual Size: A Key Distinction
One of the most important concepts to understand when working with lumber is the difference between nominal and actual dimensions. "Nominal" size is the name of the lumber (e.g., a "2x4"), which refers to its size when it was rough-sawn from the log. The "actual" size is the finished dimension after the wood has been dried and planed smooth. For instance, a nominal 2x4 is actually 1.5 inches by 3.5 inches.
For board foot calculations, you should almost always use the nominal thickness. Hardwood is typically sold based on its rough-sawn thickness (e.g., 4/4, 5/4, 8/4), so even if a 4/4 (1-inch) board is planed down to 3/4 inch, you still pay for the full 1-inch thickness. Being aware of this distinction is crucial for accurate budgeting. For more general lumber calculations that involve linear feet, you can use our versatile Lumber Calculator. For in-depth information about lumber grading and standards, the WoodBin reference guide is a fantastic resource for woodworkers of all levels.