What is a Board Foot?

A board foot is a specialized unit of measure used in the United States and Canada for the volume of lumber. It is equivalent to a volume of a board that is 12 inches wide, 12 inches long, and 1 inch thick. Understanding how to calculate board feet is essential for woodworkers, carpenters, and contractors to accurately estimate material costs and requirements for their projects.

How to Calculate Board Feet: The Formula

To calculate the board footage of a piece of lumber, you need to multiply the thickness, width, and length and then divide by a constant. The standard formula when using length in feet is:

Board Feet = (Thickness in inches × Width in inches × Length in feet) / 12

If you are measuring the length in inches instead of feet, you would divide the total by 144 instead of 12. This tool specifically uses the standard feet-based formula for ease of use in most construction contexts.

Nominal vs. Actual Dimensions

When calculating board feet, it is important to distinguish between nominal and actual sizes. For example, a standard "2x4" board is actually 1.5 inches thick and 3.5 inches wide after surfacing (planing). Most lumber yards sell wood based on its nominal size before it was planed smooth. For accurate pricing, use the nominal dimensions unless you are calculating the precise physical volume for shipping or weight constraints.

Frequently Asked Questions

Is a board foot the same as a square foot?
No. Square feet measure surface area (Length x Width), whereas board feet measure volume (Length x Width x Thickness).

What is 4/4 lumber?
In hardwood industries, thickness is often expressed in quarters. 4/4 (four-quarter) means 1 inch thick, 5/4 is 1.25 inches thick, and 8/4 is 2 inches thick.