Calculate Board Feet for Lumber

A board foot is a unit of volume used for lumber, equal to 144 cubic inches (12 inches long by 12 inches wide by 1 inch thick). Unlike square footage, which measures area, board footage measures volume. By definition, one board foot of lumber is one square foot that is one-inch thick. You use it when purchasing multiple boards of lumber in various sizes.

The board foot formula is: Board Feet = Length (ft) × Width (in) × Thickness (in) ÷ 12. Pay special attention to the units! The length should be in feet, while the width and thickness should be in inches. For example, for a board that's 8 feet long, 10 inches wide, and 1.25 inches thick: Board feet = 8 × 10 × 1.25 ÷ 12 = 8.33 BF.

Take a rectangular piece of lumber, measure the length in feet, width in inches, and thickness in inches. Then multiply all three numbers together and divide by 12. The formula is: Board Feet = (Length in feet) × (Width in inches) × (Thickness in inches) ÷ 12.

A 2x4 board is actually 1.5 inches thick and 3.5 inches wide. For different lengths: 6ft = 3.5 BF, 8ft = 4.67 BF, 10ft = 5.83 BF, 12ft = 7 BF, 16ft = 9.33 BF. Note that 2x4 boards are actually 1.5" × 3.5" in dimensions, not 2" × 4".

A board foot is a measure of volume (accounts for width, length, and thickness), while a linear foot is a measure of length only. Board feet are used for lumber pricing and are the standard unit for hardwood. Linear feet are common for trim and molding and don't account for width or thickness.

To calculate board feet in a log, you can use either the Doyle rule or the International ¼-inch rule table. Measure the diameter of the shorter end of the log (not including bark) in inches and the length in feet, then look up where the two values meet on the table. Alternative formula: ((Diameter - 4)/4)² × Length.

A board foot of oak weighs anywhere between 3.08-4.67 lb (1.42-2.12 kg), but on average, one weighs 3.875 lb (1.77 kg). This variation occurs because the density of Oak can vary from 37-56 lb/ft³ (600-900 kg/m³), depending on the variety and location it was grown.

There are no board feet in 320 square feet, as board feet is a measure of volume and square feet is a measure of area. However, for an area that is 320 square feet with a depth of 1 inch, there are 320 board feet present. Board feet measure volume while square feet measure area.

Board foot insulation is a measurement of how much volume spray foam insulation can cover. A board foot is a volume of 1 ft × 1 ft × 1 in, so you estimate the volume you need to fill before buying your spray foam insulation by finding the square footage of the space. A board foot is also a common unit of measure for lumber in the USA and Canada.