Add 10–15% for offcuts, defects, and trimming. Use actual board dimensions, not nominal sizes, for the most accurate result.
What Is a Board Foot and How Is It Calculated?
A board foot is the standard unit of lumber volume in the US and Canada. One board foot equals a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick, which works out to 144 cubic inches. Most hardwood lumber is priced per board foot, and many softwood suppliers also use it for pricing larger orders or random-width stock.
The formula is: thickness in inches, multiplied by width in inches, multiplied by length in feet, multiplied by quantity, all divided by 12. That division by 12 converts the result from cubic inches per foot of length into the board-foot standard. A 2-inch thick, 6-inch wide, 10-foot board is (2 x 6 x 10) / 12 = 10 board feet.
Nominal vs Actual Dimensions
This is where most people make mistakes. Dimensional lumber is sold by nominal size but measures smaller once it has been dried and surfaced. A nominal 2x6 actually measures about 1.5 inches by 5.5 inches. If you use nominal dimensions, you'll overestimate the board footage. For lumber already in hand or for hardwood orders where you're quoting from actual measurements, use the actual dimensions. For ordering dimensional softwood by the piece, nominal dimensions are typically what suppliers use for pricing.
| Nominal Size | Actual Size | Board Ft per 8 ft length |
|---|---|---|
| 1x4 | 0.75" x 3.5" | 2.67 (nominal) / 1.75 (actual) |
| 1x6 | 0.75" x 5.5" | 4.0 (nominal) / 2.75 (actual) |
| 2x4 | 1.5" x 3.5" | 5.33 (nominal) / 3.5 (actual) |
| 2x6 | 1.5" x 5.5" | 8.0 (nominal) / 5.5 (actual) |
| 2x8 | 1.5" x 7.25" | 10.67 (nominal) / 7.25 (actual) |
| 4x4 | 3.5" x 3.5" | 10.67 (nominal) / 8.17 (actual) |
How Much Waste to Add
For straight cuts and simple framing work, 10% is usually enough. It covers the occasional board with a knot or warp that you can't use, plus the small offcuts at the end of each run. For fine woodworking with tight grain matching or complex joinery, 15% is more realistic. For rough-sawn hardwood where you're also surfacing the lumber yourself, up to 20% accounts for material lost to the planer and jointer. Decking projects with lots of angle cuts at the perimeter also benefit from the higher end of the range.
When Board Feet Are Used
Hardwood suppliers almost always quote by the board foot. When you're buying oak, walnut, maple, or cherry for furniture or cabinetry, you'll need to know your total board footage to get a price. Softwood suppliers more often sell by the lineal foot or by the piece, but for large framing orders or custom milling, board foot pricing is common there too. Decking, trim, and moulding are usually quoted by the lineal foot rather than by board foot.
Frequently Asked Questions
Lumber Project Planning Checklist
Before placing your lumber order, confirm framing layout, joist spacing, hardware requirements, and whether you need kiln-dried or green lumber for your application.
Download Checklist (PDF)Planning use only. See Methodology and Data Sources. View all project checklists →
Accuracy & Review
Reviewed by: Liam Santos
Liam reviews decking, lumber, and board foot calculators to confirm accurate framing takeoffs, dimensional lumber calculations, and waste assumptions. He focuses on ensuring estimates reflect practical framing layouts and real-world material usage.
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See: Methodology · Data Sources · Review Board
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Disclaimer
These estimates are for general planning purposes only and should not be used as structural design guidance. Actual lumber quantities depend on span limits, load requirements, material grade, and building code compliance.
Structural framing components should be verified against current code requirements before construction. Always confirm quantities with your lumber supplier before ordering.
See our Methodology and Data Sources for details.