How to Calculate Board Foot of Lumber
A simple and accurate tool for woodworkers, builders, and hobbyists.
Enter the actual thickness of the board in inches.
Enter the actual width of the board in inches.
Enter the actual length of the board.
Enter the number of identical boards.
Total Cubic Inches: 0
Volume in Cubic Feet: 0.000
Board Feet vs. Length
What is a Board Foot?
A board foot (BF or bd. ft.) is the fundamental unit of volume for lumber in the United States and Canada. It represents a piece of wood that is one foot long, one foot wide, and one inch thick. Essentially, one board foot is equivalent to 144 cubic inches of wood (12″ × 12″ × 1″). This measurement is crucial for anyone buying or selling rough-sawn or hardwood lumber, as it standardizes the pricing and estimation process regardless of the individual board’s dimensions. Understanding how to calculate board foot of lumber ensures you can accurately budget for projects and verify you’re getting the right amount of material.
The Board Foot Formula and Explanation
There are two common formulas to calculate board foot, depending on the units you use for length. The most widely used formula, and the one our calculator employs, is for a length measured in feet:
Board Feet = (Thickness in Inches × Width in Inches × Length in Feet) / 12
If you measure the length in inches, you would divide by 144 instead:
Board Feet = (Thickness in Inches × Width in Inches × Length in Inches) / 144
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Thickness (T) | The thickness of the lumber plank. For hardwoods, this is often expressed in quarters (e.g., 4/4 for 1″, 8/4 for 2″). | Inches | 0.75″ – 4″ |
| Width (W) | The width of the lumber plank. | Inches | 2″ – 12″+ |
| Length (L) | The length of the lumber plank. | Feet (or Inches) | 4′ – 16′ |
Practical Examples
Example 1: A Standard Dimensional Board
Let’s say you want to find the board footage of a common “2×6” that is 8 feet long. It’s critical to use the actual dimensions, not the nominal ones. A nominal 2×6 is actually 1.5″ thick and 5.5″ wide.
- Inputs: T = 1.5″, W = 5.5″, L = 8′
- Formula: (1.5″ × 5.5″ × 8′) / 12
- Result: 5.5 Board Feet
Example 2: A Piece of Hardwood
Imagine you’re buying a piece of rough-sawn walnut for a tabletop. You measure it to be 2 inches thick, 10 inches wide, and 6 feet long.
- Inputs: T = 2″, W = 10″, L = 6′
- Formula: (2″ × 10″ × 6′) / 12
- Result: 10 Board Feet
If you plan a project, you might find our guide to buying rough lumber helpful for budgeting.
How to Use This Board Foot Calculator
- Measure Thickness: Using a tape measure, find the actual thickness of your board in inches and enter it into the “Thickness (T)” field.
- Measure Width: Measure the actual width of the board in inches and enter it into the “Width (W)” field.
- Measure Length: Measure the length of the board. You can enter this value in either feet or inches by selecting the correct unit from the dropdown.
- Enter Quantity: If you have multiple boards of the exact same dimensions, enter the total number in the “Quantity” field.
- Interpret the Results: The calculator will instantly show you the total board feet. It also provides intermediate values like total cubic inches and cubic feet for additional context.
Key Factors That Affect Board Foot Calculations
- Nominal vs. Actual Size: This is the most common point of confusion. Always use the actual, measured dimensions of a board for an accurate board foot calculation, not the nominal size (e.g., “2×4”). Surfacing and drying reduce the rough-sawn size to its final dimensions.
- Measurement Units: Ensure consistency. The standard formula requires thickness and width in inches and length in feet. Using the wrong units without adjusting the formula will lead to incorrect results.
- Rough vs. Surfaced Lumber: Board foot calculations are typically based on the rough-sawn dimensions before the wood is planed smooth. For projects requiring precise final thickness, consider checking out a lumber volume calculator to account for material loss.
- Fractional Measurements: Hardwood thickness is often sold in quarter-inch increments, like 4/4 (four-quarter), 5/4, or 8/4. A 4/4 board is nominally 1″ thick. Our calculator accepts decimal inputs for simplicity.
- Wane and Defects: Board foot calculations assume a rectangular piece of wood. If a board has significant wane (missing wood on the edges) or other defects, you are still paying for the volume of the smallest rectangular block that the board would fit into.
- Length Rounding Rules: In the hardwood industry, the National Hardwood Lumber Association (NHLA) rules often dictate rounding the length down to the nearest foot. For most DIY and smaller-scale purposes, using the exact length is sufficient.
Frequently Asked Questions (FAQ)
1. What’s the difference between a board foot and a linear foot?
A board foot is a measure of volume, while a linear foot is simply a measure of length. A 12-foot long board is 12 linear feet, but its board footage depends on its thickness and width.
2. Is a board foot a measure of length, area, or volume?
It is a measure of volume. One board foot occupies a volume of 144 cubic inches.
3. How do I calculate board feet for multiple pieces?
Calculate the board footage for a single piece and then multiply that result by the total number of identical pieces. Our calculator does this automatically with the “Quantity” field.
4. Why must I use actual dimensions instead of nominal for the calculation?
Nominal dimensions (like “2×4″) are the size of the board before it’s dried and planed. The actual dimensions are what you physically have. Using nominal sizes will incorrectly inflate the board foot result. For example, a nominal 2×4 (1.5″x3.5″) is 33% smaller by volume than a full 2″x4”. For custom projects like building a deck, using actual dimensions is critical for accurate material ordering.
5. How do I convert board feet to cost?
Multiply the total board feet by the price per board foot. For example, if you need 20 board feet and the lumber costs $8 per board foot, your total cost would be $160 (20 BF * $8/BF).
6. Does the type of wood affect the board foot calculation?
No, the board foot calculation is purely a measure of volume and is independent of the wood species. However, the price per board foot varies significantly between species. You can explore different options with our guide on choosing hardwoods.
7. What if my board is not perfectly rectangular?
For irregularly shaped boards, you typically measure the average width and use the standard formula. This provides a reasonable estimate for most practical purposes.
8. Why does the formula divide by 12?
The division by 12 converts the volume from a unit of “inch × inch × foot” into the standard board foot unit. It accounts for the fact that you are multiplying two measurements in inches by one in feet.