A board foot is the standard unit of measurement used to quantify the volume of lumber, particularly when purchasing hardwood or rough-sawn timber. While "lumber foot" might be used informally, "board foot" is the correct and widely recognized industry term.
Understanding the Board Foot
A board foot represents a specific volume of wood. It is equivalent to a piece of lumber that is one inch thick, one foot wide, and one foot long. This specific dimension translates to a total volume of 144 cubic inches.
This volumetric measurement is crucial because lumber is not always sold by its length (linear feet) or surface area (square feet). Instead, its value is often determined by the actual amount of wood material it contains, regardless of its specific cut or dimensions, making the board foot an essential unit for fair pricing and inventory management.
Why is Lumber Measured in Board Feet?
Lumber dimensions vary significantly in thickness, width, and length. Using a volumetric unit like the board foot provides a standardized way to price and compare different pieces of wood based on their total material content rather than just their face dimensions or length. This system is particularly beneficial for:
- Hardwood Lumber: Hardwood lumber is almost exclusively sold by the board foot, especially when it's rough-sawn or ungraded.
- Rough Lumber: Untrimmed or undressed lumber, where the exact finished dimensions might vary, is best measured by volume.
- Consistent Pricing: It allows suppliers to price wood consistently, considering the actual wood volume rather than just linear measurements, which can be misleading for different thicknesses.
Calculating Board Feet
Calculating the number of board feet in a piece of lumber involves a simple formula. The most common formula is:
(Thickness in inches × Width in inches × Length in feet) / 12
Alternatively, you can use:
(Thickness in inches × Width in feet × Length in feet)
It's important to remember that for softwood and some construction lumber, nominal dimensions (e.g., a "2x4" which is actually 1.5" x 3.5") are often used for board foot calculations, though hardwood is typically calculated based on its actual, rough dimensions.
Practical Calculation Examples:
Let's calculate the board feet for a few common lumber dimensions:
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Example 1: A 1-inch thick, 6-inch wide, and 12-foot long board
- (1" × 6" × 12') / 12 = 6 board feet (BF)
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Example 2: A 2-inch thick, 4-inch wide, and 8-foot long board (like a nominal 2x4)
- (2" × 4" × 8') / 12 = 5.33 board feet (BF)
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Example 3: A 3-inch thick, 10-inch wide, and 16-foot long timber
- (3" × 10" × 16') / 12 = 40 board feet (BF)
Common Board Foot Equivalents
Understanding common board foot equivalents can help in quick estimations:
| Nominal Dimensions (Thickness x Width) | Board Feet per Linear Foot |
|---|---|
| 1" x 4" | 0.33 BF |
| 1" x 6" | 0.5 BF |
| 1" x 8" | 0.67 BF |
| 1" x 10" | 0.83 BF |
| 1" x 12" | 1.0 BF |
| 2" x 4" | 0.67 BF |
| 2" x 6" | 1.0 BF |
| 2" x 8" | 1.33 BF |
| 2" x 10" | 1.67 BF |
| 2" x 12" | 2.0 BF |
| 4" x 4" | 1.33 BF |
Distinguishing from Other Lumber Measurements
It's important not to confuse board feet with other common lumber measurements:
- Linear Foot: Measures only the length of the board. A 2x4 that is 10 feet long is 10 linear feet, but its board footage is different.
- Square Foot: Measures the surface area (length x width) of a board, typically used for thin sheet goods like plywood or paneling, where thickness is standard.
By understanding the board foot, consumers and professionals can accurately assess and compare the volume and cost of various lumber products.
