Lumber Board-Feet Calculator
Calculate the board footage of any lumber piece or order by entering the thickness, width, length, and quantity to get precise measurements and cost estimates.
What is Lumber Board-Feet?
A board foot is the standard unit of measurement for hardwood lumber in North America. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long, or equivalently, 144 cubic inches of wood. Understanding board feet is essential for purchasing hardwood lumber, which is almost always priced and sold by the board foot rather than by the linear foot. The board foot system dates back to early American sawmills and remains the industry standard for rough-sawn hardwood lumber. Softwoods like dimensional lumber (2x4s, 2x6s) are typically sold by the linear foot at home improvement stores, but hardwood dealers, specialty lumber yards, and sawmills price their inventory in board feet. The formula is straightforward: multiply the thickness in inches by the width in inches by the length in feet, then divide by 12. This gives you the volume of wood in board feet. For example, a board that is 1 inch thick, 8 inches wide, and 10 feet long contains 6.67 board feet. When purchasing rough-sawn lumber, the nominal thickness is used for calculation. A board sold as 4/4 (four-quarter) is nominally 1 inch thick, 5/4 is 1.25 inches, 6/4 is 1.5 inches, 8/4 is 2 inches, and so on. After surfacing (planing), the actual thickness will be approximately 1/8 to 1/4 inch less than the nominal size. Pricing per board foot varies dramatically depending on species, grade, and availability. Common domestic hardwoods like red oak or poplar may cost $3-7 per board foot, while exotic species like purpleheart or zebrawood can run $12-25 or more per board foot. Wider and longer boards often command a premium since they are less common and more versatile for furniture making. Always add 15-25 percent to your calculated board footage to account for waste from cutting, defects, and mistakes. Most lumber yards require a minimum purchase and may charge differently for select versus common grades.
How to Calculate
- Measure or note the thickness of the board in inches (use nominal thickness for rough lumber)
- Measure or note the width of the board in inches
- Measure or note the length of the board in feet
- Enter the number of identical pieces you need
- Enter the price per board foot from your lumber supplier (optional, for cost estimate)
- Review the board feet per piece, total board footage, and estimated cost
Formula
Board Feet = (Thickness in inches x Width in inches x Length in feet) / 12 Total Board Feet = Board Feet per Piece x Number of Pieces Estimated Cost = Total Board Feet x Price per Board Foot The division by 12 converts the result from cubic inches (with length in feet) to the standard board foot unit. One board foot equals 144 cubic inches, and since length is already in feet (12 inches), we only divide by 12 rather than 144.
Example Calculation
Calculate the board footage and cost for 6 pieces of 8/4 walnut, each 6 inches wide and 8 feet long, at $12 per board foot: Thickness = 2 inches (8/4 lumber) Width = 6 inches Length = 8 feet Board Feet per Piece = (2 x 6 x 8) / 12 = 96 / 12 = 8 BF Total Board Feet = 8 x 6 pieces = 48 BF Estimated Cost = 48 x $12 = $576.00
Frequently Asked Questions
What does 4/4, 5/4, 8/4 mean for lumber thickness?
These fractions represent quarters of an inch in nominal thickness. 4/4 means four quarters or 1 inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. After surfacing, actual thickness is typically 1/8 to 1/4 inch less.
Do I use nominal or actual dimensions for board feet?
Use nominal (rough-sawn) dimensions when buying rough lumber, as that is how it is measured and priced. If buying surfaced lumber (S2S or S4S), the dealer has already calculated the board feet based on the pre-surfaced nominal size.
How much waste should I add to my board foot estimate?
Add 15-25 percent for typical woodworking projects to account for cutting waste, defects in the wood, and potential mistakes. For complex projects with many angled cuts, consider adding up to 30 percent.
Is a board foot the same as a linear foot?
No. A linear foot measures only length regardless of width and thickness. A board foot measures volume (thickness x width x length / 12). A single 12-foot board could contain anywhere from 2 to 24 board feet depending on its width and thickness.
Why is hardwood sold by board feet instead of linear feet?
Hardwood boards come in random widths and lengths from the sawmill, unlike dimensional softwood lumber which is milled to standard sizes. Board feet provides a fair volumetric measurement regardless of the random dimensions of each piece.
How do I calculate board feet for a round or irregular piece?
For round logs, use the diameter as the width. For irregular pieces, use the average width measured at several points along the board. Lumber dealers will also measure waney-edge (live-edge) boards at their narrowest usable width.