Board Foot Calculator Guide: What Is a Board Foot?
Understand board feet, how to calculate lumber quantities, and when to use board feet vs. linear feet for your project.
If you’ve ever priced hardwood at a lumber yard, you’ve encountered the board foot. Unlike the linear foot (which only measures length), the board foot accounts for width and thickness — it’s a measure of volume, not just length. Understanding it is essential for pricing lumber accurately and communicating with suppliers.
Quick Answer: Board Feet = (Thickness × Width × Length in feet) ÷ 12. Use nominal dimensions (a 2×4 counts as 2×4, not 1.5×3.5). Hardwood is always priced in board feet; dimensional framing is priced in linear feet. When in doubt, ask your supplier which unit their quote uses.
What Is a Board Foot?
A board foot is equal to 144 cubic inches of lumber. The most intuitive way to think about it: a board foot is a piece of wood 1 inch thick, 12 inches wide, and 12 inches long.
Formula: Board Feet = (Thickness (inches) × Width (inches) × Length (feet)) ÷ 12
Or equivalently, using length in inches: Board Feet = (Thickness × Width × Length) ÷ 144
Board Foot Examples
| Dimension | Length | Board Feet |
|---|---|---|
| 1×4 | 8 ft | 2.67 BF |
| 1×6 | 8 ft | 4 BF |
| 1×12 | 8 ft | 8 BF |
| 2×4 | 8 ft | 5.33 BF |
| 2×6 | 8 ft | 8 BF |
| 2×8 | 10 ft | 13.33 BF |
| 4×4 | 10 ft | 13.33 BF |
Use our Board Foot Calculator to calculate any combination instantly.
Nominal vs. Actual Lumber Dimensions
Here’s a critical detail: board feet are calculated using nominal dimensions, not actual dimensions. A 2×4 is actually 1.5” × 3.5”, but for board foot calculations you use 2 × 4.
This is a longstanding convention in the lumber industry. When a supplier quotes a price per board foot, they’re using nominal dimensions. When you calculate structural capacity, use actual dimensions.
When Board Feet Matter Most
Hardwood Purchasing
Hardwoods (oak, maple, walnut, cherry) are almost always sold and priced by the board foot. A board foot of walnut might cost $10–$20+. Knowing your board foot count before you shop is essential to budgeting.
Large Framing Orders
For big framing packages (an entire house or addition), lumber yards often quote by the board foot on total packages. Having your own estimate lets you verify the quote.
Custom Millwork
Custom moulding, trim, and casework is often quoted by the board foot for material cost.
Log and Timber Sales
Rough-sawn lumber from local sawmills is priced by the board foot. If you’re buying green timber or having logs custom-sawn, board feet is the standard unit.
Board Feet vs. Linear Feet
Linear feet only measure length. They’re used for:
- Ordering dimensional framing lumber (2×4, 2×6, etc.)
- Trim, moulding, and baseboard
- Decking boards (counted by piece, measured in linear feet)
Board feet measure volume. They’re used for:
- Hardwood purchasing
- Timber and heavy structural lumber
- Any situation where you’re comparing prices across different dimensions
If a supplier quotes framing lumber at $0.70 per board foot and you have 1,000 board feet of 2×4s, you’re paying $700. If another supplier quotes $0.50 per linear foot and you have 500 linear feet of 2×4s, that’s $250. Board feet let you compare apples to apples across different sizes.
Waste Factor for Lumber
When calculating how many board feet to order, add a waste factor:
| Application | Waste Allowance |
|---|---|
| Rough framing | 10–15% |
| Trim and moulding | 15–20% |
| Hardwood furniture | 20–30% |
| Live edge / figured wood | 25–40% |
For hardwood especially, you’ll lose significant material to defects, checks, and irregular edges on rough-sawn boards.
Frequently Asked Questions
Why is a 2×4 not actually 2 inches × 4 inches? Dimensional lumber is milled oversized (green) and then dried and planed, which reduces it to final dimensions. A 2×4 rough-sawn is close to 2×4; the finished, planed board is 1.5×3.5. The nominal name stuck from historical convention.
How do I calculate board feet for a project with many different lumber sizes? Calculate board feet for each distinct size separately, then sum them. Our Board Foot Calculator handles multiple pieces at once.
Does the board foot price include the cost of surfacing? Rough-sawn lumber costs less per board foot but requires more work. S4S (surfaced four sides) costs more per BF but is ready to use. Make sure you’re comparing apples to apples when pricing.
What’s an MBF? An MBF is 1,000 board feet — a common wholesale unit. Large lumber orders are often quoted per MBF. Divide the MBF price by 1,000 to get the per-board-foot price.
See also: Framing Calculation Methodology — IRC R602 references, stud count formulas, and lumber waste factors behind ConstructCalc framing calculators.
Browse more