Board size is primarily measured using the board foot, a standard unit of lumber volume.
A board foot represents a volume equivalent to a board measuring 1 inch thick, 12 inches wide, and 1 foot long. While actual lumber dimensions can vary slightly due to milling and drying, board footage is calculated using nominal dimensions (the size before drying and planing) for thickness and width, combined with the actual length in feet.
Calculating Board Footage
The standard method for calculating board footage is based on the nominal dimensions of the lumber. This is crucial for pricing and estimating quantities in the lumber industry.
According to common practice and the provided reference, the formula for calculating board footage is:
Board Foot (ft.) = (Nominal Thickness in Inches × Nominal Width in Inches × Actual Length in Feet) / 12
Or, using the variables from the reference:
T x W x L = Board ft.
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Where:
- T = Nominal Thickness in inches
- W = Nominal Width in inches
- L = Actual Length in feet
Understanding Nominal vs. Actual Dimensions
Lumber is often referred to by its nominal size (e.g., "2x4" or "4x8"). These are the dimensions of the board before it is dried and surfaced (planed smooth). The actual dimensions are slightly smaller. However, board footage calculations typically use the nominal thickness (T) and width (W) as part of the formula, alongside the actual length (L).
Example Calculation
The provided reference states: "For instance a 2 x 6 also equals one board foot for each foot of length." Let's verify this using the formula:
- Nominal Thickness (T): 2 inches
- Nominal Width (W): 6 inches
- Actual Length (L): 1 foot
Calculation:
(2 inches × 6 inches × 1 foot) / 12 = (12 × 1) / 12 = 12 / 12 = 1 board foot
This confirms that a 2x6 board contains 1 board foot for every foot of its actual length. A 2x6 board 8 feet long would contain 8 board feet (1 board foot/foot * 8 feet = 8 board feet).
Practical Applications
Understanding board footage is essential for:
- Pricing: Lumber is often sold by the board foot.
- Estimating: Calculating the total volume of lumber needed for a project.
- Inventory Management: Tracking lumber quantities in a yard or warehouse.
Here are a few more examples of board footage calculations:
| Nominal Size (T x W) | Actual Length (L) | Calculation (T x W x L / 12) | Board Footage |
|---|---|---|---|
| 1 x 12 | 10 feet | (1 x 12 x 10) / 12 | 10 bf |
| 4 x 8 | 6 feet | (4 x 8 x 6) / 12 | 16 bf |
| 2 x 4 | 12 feet | (2 x 4 x 12) / 12 | 8 bf |
While length and actual width/thickness can be measured with a tape measure, calculating the 'size' in terms of total volume typically refers to determining the board footage using this standard formula.
