BF stands for “board foot,” the standard unit of measurement for lumber volume in the United States and Canada. One board foot equals a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick, or 144 cubic inches total. It’s the unit you’ll encounter most often when buying hardwood or pricing lumber for a project.
What a Board Foot Actually Measures
Unlike linear feet (which measure length) or square feet (which measure area), a board foot measures volume. It captures all three dimensions of a board: thickness, width, and length. This matters because lumber, especially hardwood, comes in random widths and lengths. A board foot gives buyers and sellers a fair, standardized way to compare and price boards of different sizes.
Think of it this way: a board that’s 1 inch thick, 6 inches wide, and 2 feet long contains exactly 1 board foot. So does a board that’s 2 inches thick, 3 inches wide, and 2 feet long. The shapes are different, but the volume of wood is the same.
How to Calculate Board Feet
The formula is straightforward:
Thickness (inches) × Width (inches) × Length (feet) ÷ 12 = Board Feet
For example, a board that’s 1 inch thick, 8 inches wide, and 6 feet long would be: 1 × 8 × 6 ÷ 12 = 4 board feet.
One important detail: the calculation uses nominal thickness and width, not actual dimensions. A “1-inch” board that’s been planed down to 3/4 inch is still calculated as 1 inch for board footage purposes. This is the same reason a 2×4 from the hardware store actually measures 1.5 × 3.5 inches but is sold under its nominal name.
Hardwood Thickness and the Quarter System
If you’re shopping for hardwood, you’ll often see thickness listed in quarters of an inch rather than whole numbers. A board labeled 4/4 (said “four-quarter”) is 1 inch thick. An 8/4 board is 2 inches thick. These refer to the rough-sawn thickness before any planing or surfacing.
The quarter system plugs directly into the board foot formula. A 4/4 board uses 1 as the thickness. An 8/4 board uses 2. So an 8/4 board with the same width and length as a 4/4 board contains exactly twice the board footage.
Board Feet vs. Linear and Square Feet
- Linear feet measure only length. Lumber yards use this for wood cut to standard, uniform dimensions, like common framing lumber (2×4s, 2×6s) where thickness and width are already known.
- Square feet measure area (length × width). This is typically used for lumber thinner than 1 inch, like veneers and thin panels.
- Board feet measure volume. This is the go-to unit for hardwood lumber that comes in random widths and lengths, since it accounts for all three dimensions in a single number.
If you’re buying dimensional lumber at a big-box store, you’ll usually see prices per piece or per linear foot. Walk into a hardwood dealer, and nearly everything is priced per board foot.
How Pricing Works Per Board Foot
Lumber yards price species by the board foot. Cherry might run $9 per board foot, while walnut or maple could be higher or lower depending on grade, availability, and whether it’s been kiln-dried. To estimate your material cost, multiply the total board feet you need by the price per board foot. Twenty board feet of cherry at $9/BF comes out to $180.
Prices also shift based on quality. Boards with fewer knots, straighter grain, and less warping command higher prices. Kiln-dried lumber costs more than green (freshly cut) wood because the drying process adds time, energy, and reduces the board’s weight.
Adding a Waste Factor to Your Estimate
Raw lumber is never perfectly usable from end to end. Knots, splits, warped sections, and sapwood all reduce the amount of clean material you can actually use. The standard practice is to add 15% to 20% to your calculated board footage to account for these defects. If you’re working with lower-grade lumber or planning a project that demands long, clear pieces, bumping that buffer to 25% or even higher is reasonable.
For a project that needs 100 board feet of usable wood, plan to purchase at least 115 to 120 board feet. This avoids a second trip to the lumber yard and ensures you have enough material to work around imperfections.