Board Feet Calculator
Calculate board feet for lumber using nominal dimensions. Supports single piece, multiple identical pieces, and mixed orders with optional price per board foot.
What is a Board Foot?
A board foot (BF) is the standard unit of volume used to measure and price lumber in North America. One board foot equals 144 cubic inches, which is the volume of a board that measures 1 inch thick, 12 inches wide, and 12 inches long. Lumberyards and hardwood dealers quote prices per board foot, making this calculator essential for accurately estimating material costs for any woodworking or construction project.
How to Calculate Board Feet
The board feet formula is simple: multiply the nominal thickness in inches by the nominal width in inches by the length in feet, then divide by 12. The formula is BF = (T x W x L) / 12, where T is thickness in inches, W is width in inches, and L is length in feet. For multiple identical pieces, multiply the single-piece BF by the quantity. For mixed orders, calculate each row separately and add the totals together.
Nominal vs Actual Lumber Dimensions
Lumber is sold by its nominal (labeled) dimensions, not its actual planed size. A 2 x 4 board is labeled as 2 inches by 4 inches but actually measures 1.5 inches by 3.5 inches after planing and drying. Board foot calculations always use nominal dimensions for pricing. The American Lumber Standards Committee (ALSC) standardizes these reductions under PS 20, ensuring consistency across all lumberyards.
Common nominal-to-actual conversions include: 1-inch nominal becomes 0.75 inches actual, 2-inch nominal becomes 1.5 inches actual, and 4-inch nominal becomes 3.5 inches actual. Widths up to 6 inches lose 0.5 inches, while widths 8 inches and above lose 0.75 inches.
Board Feet vs Linear Feet vs Square Feet
These three units measure different things. A board foot is a volume unit (144 cubic inches). A linear foot (also called lineal foot) measures length only, regardless of cross-section. A square foot measures area. Lumberyards quote softwood dimensional lumber by the piece or linear foot, but hardwood and rough-cut lumber are priced by the board foot because cross-sections vary. Always confirm with your dealer which unit you are being quoted.
Frequently Asked Questions
What is a board foot?
A board foot (BF) is a unit of lumber volume equal to 144 cubic inches. It represents the volume of a board 1 inch thick, 12 inches wide, and 12 inches long. The formula is BF = (thickness in inches x width in inches x length in feet) / 12.
How many board feet are in a 2x4 by 8 feet?
A 2 x 4 x 8 ft board contains 5.333 board feet. The calculation is (2 x 4 x 8) / 12 = 64 / 12 = 5.333 BF. This uses nominal dimensions, so the result is the lumberyard's billing figure.
What is the difference between nominal and actual lumber sizes?
Nominal size is the label dimension (like 2x4), while actual size is what you measure after planing and drying. A 2x4 actually measures 1.5 inches by 3.5 inches. Board foot calculations always use nominal dimensions for pricing, but you need actual dimensions for layout and clearance.
How do I calculate lumber cost from board feet?
Multiply the total board feet by the price per board foot. For example, 50 BF of red oak at $6.75 per BF costs 50 x $6.75 = $337.50. Our calculator includes an optional price input to show cost alongside the board foot total.
Should I add a waste factor when ordering lumber?
Yes. For hardwood projects, add 10-20% more BF than your cut list calls for to account for checking, knots, and sapwood. For dimensional softwood used in framing, a 5-10% overage handles bad cut-offs and on-site mistakes. Use the mixed-order mode to add a buffer row.
How is hardwood thickness measured?
Hardwood is sold in quarter-inch increments: 4/4 (1 inch), 5/4 (1.25 inches), 6/4 (1.5 inches), 8/4 (2 inches), and so on. The calculator accepts both standard softwood sizes and hardwood quarter thicknesses for maximum flexibility.
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