Board Feet Calculator
Calculate the volume of a lumber board in board feet — the standard unit for buying and selling wood. Use it when pricing lumber orders or estimating material needs for woodworking projects.
About this calculator
A board foot is a unit of lumber volume equal to 144 cubic inches — the equivalent of a 1-inch-thick board that is 12 inches wide and 12 inches long. The formula is: Board Feet = (Length × Width × Thickness) / 144, where all three dimensions are measured in inches. Because lumber is sold by the board foot rather than by the piece, knowing this value lets you compare prices across different species and sizes. Thickness matters even for standard dimensional lumber: a 2×4 is actually 1.5 inches thick, so always use the actual measured dimension rather than the nominal size. This calculation is essential when budgeting a large project, such as building cabinets or flooring a room, where small per-unit price differences multiply across dozens of boards.
How to use
Suppose you have a walnut plank that is 96 inches long, 8 inches wide, and 1.5 inches thick. Plug the values into the formula: Board Feet = (96 × 8 × 1.5) / 144. First multiply the dimensions: 96 × 8 = 768, then 768 × 1.5 = 1,152. Divide by 144: 1,152 / 144 = 8 board feet. That single plank contains 8 bf. If walnut costs $12 per board foot, this plank would cost $96 before tax. Repeat for each board and sum the results to get your total order volume.
Frequently asked questions
What is a board foot and why is lumber sold in board feet?
A board foot is a volumetric unit equal to 144 cubic inches, commonly represented as a 1″ × 12″ × 12″ piece of wood. Lumber is sold this way because boards come in wildly different widths and thicknesses, and a volume-based unit allows fair price comparison across all of them. It originated in the timber trade as a practical standard long before metric systems were common in North America. Hardwood retailers in particular price almost exclusively in board feet, so understanding the unit is essential for any woodworker sourcing material.
How do I calculate board feet when lumber dimensions are given in feet instead of inches?
If your length is in feet but width and thickness are in inches, convert everything to inches first by multiplying feet by 12. Alternatively, use the feet-based variant of the formula: Board Feet = (Length_ft × Width_in × Thickness_in) / 12. Both approaches yield the same result — just be consistent with your units. Many online lumber dealers list length in feet and width in inches, so keeping track of units is the most common source of errors in this calculation.
Why does nominal lumber size differ from actual size when calculating board feet?
Nominal sizes (like 2×4 or 1×6) reflect the rough-cut dimensions before the board is dried and planed smooth at the mill. After milling, a 2×4 is actually about 1.5″ × 3.5″. When calculating board feet for cost purposes, hardwood yards typically charge on the rough or nominal dimension, while home-improvement stores may charge on actual dimensions. Always confirm which convention your supplier uses before calculating, because using the wrong thickness can cause a 10–30% error in your estimate.