Board Feet Calculator
Enter lumber dimensions to calculate board feet. Build a project materials list, add a kerf waste allowance, and get a cost estimate at your entered price per board foot. Nominal vs. actual size guide included. Nothing uploaded.
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Learn more: board feet and lumber calculations
The formula: from dimensions to board feet
Board feet = (thickness in inches x width in inches x length in inches) / 144. A 2x4 that is 8 feet long calculates as (1.5 x 3.5 x 96) / 144 = 3.5 board feet. This formula assumes you are using actual dressed dimensions, not the nominal size marked on the lumber.
Nominal vs actual lumber sizes
Nominal size is the name of the lumber as sold: 2x4, 1x6, 4x4. Actual size is the physical dimension after the lumber is dried and planed smooth. A nominal 2x4 is actually 1.5 inches x 3.5 inches. The calculator includes presets for all standard sizes, but for custom lumber always measure the actual dimensions rather than assuming nominal.
Building a project materials list
Enter each board in your project with its species or label, length, width, thickness, and quantity. The calculator totals all board feet across every piece. This helps you know exactly how much to order before visiting the timber yard, avoiding both under-ordering (which risks a second delivery from a different batch with colour mismatch) and over-ordering (which wastes expensive materials).
Kerf waste and sawing loss
The kerf is the width of material removed by a saw blade during each cut - typically 1/8 inch (3mm) for standard circular saw blades. When ripping multiple pieces, the kerf waste accumulates. Add 5-10% to your board feet total to account for this loss plus any rough crosscut allowances. The calculator has a kerf waste percentage field to adjust for your specific sawing method.
Why the nominal-to-actual gap grows for wider boards
The gap between nominal and actual size is not a flat 1/2 inch across every width. For boards up to 6 inches nominal, the actual width runs 1/2 inch under nominal: a 1x6 is really 5.5 inches. Once boards reach 8 inches nominal and wider, the gap grows to 3/4 inch: a 1x8 or 2x8 is actually 7.25 inches, not 7.5.
Wider boards lose more material to shrinkage and surfacing during drying and planing, so mills settled on a bigger deduction at the wider sizes instead of one flat offset. Assuming every board loses the same 1/2 inch will overstate your board feet on anything 8 inches wide or larger.
Comparing cost per board foot across species and grades
Board feet is the unit that lets you compare price fairly between boards of different thickness, width, and length, since a 2x4 and a 2x10 of the same length contain very different volumes of wood. Dividing a board's price by its board-foot count gives a cost-per-board-foot figure you can put side by side against a different board, species, or supplier.
This matters most when comparing a cheaper common-grade board against a pricier select or clear-grade board of the same species. The wider or higher-grade board is not automatically worse value: converting both to cost per board foot is what actually shows which is the better deal for the amount of usable wood you are paying for.
FAQ
How do I calculate board feet?
Board feet = (thickness in inches x width in inches x length in inches) / 144. For example, a 2x4 that is 8 feet long: (1.5 x 3.5 x 96) / 144 = 3.5 board feet. Always use actual dimensions, not nominal.
What is the difference between nominal and actual lumber size?
Nominal size is the name of the lumber (2x4, 1x6) as sold. Actual size is the physical dimension after the lumber is dried and planed smooth. A nominal 2x4 is actually 1.5 inches x 3.5 inches. Board feet calculations must always use actual dimensions for accuracy.
What is kerf waste in woodworking?
The kerf is the width of material removed by a saw blade during each cut - typically 1/8 inch (3mm) for standard circular saw blades. When ripping multiple pieces, the kerf waste accumulates. Adding 5-10% to your board feet total accounts for this loss plus any rough crosscut allowances.