Board Foot Calculator
Easily calculate the board feet of your lumber. Enter the dimensions below to get the result. This tool helps you understand how to calculate a board foot accurately.
Board Feet vs. Thickness (for current Width & Length)
Chart showing how board feet change with thickness, keeping width and length constant as entered.
Common Lumber Sizes and Board Feet
| Nominal Size (inches) | Length (feet) | Board Feet |
|---|---|---|
| 1 x 4 | 8 | 2.67 |
| 1 x 6 | 8 | 4.00 |
| 1 x 8 | 8 | 5.33 |
| 1 x 10 | 8 | 6.67 |
| 1 x 12 | 8 | 8.00 |
| 2 x 4 | 8 | 5.33 |
| 2 x 6 | 8 | 8.00 |
| 2 x 8 | 8 | 10.67 |
| 2 x 10 | 8 | 13.33 |
| 2 x 12 | 8 | 16.00 |
| 1 x 6 | 10 | 5.00 |
| 2 x 4 | 10 | 6.67 |
| 1 x 6 | 12 | 6.00 |
| 2 x 4 | 12 | 8.00 |
Table showing approximate board feet for common nominal lumber dimensions at various lengths.
What is a Board Foot?
A board foot (BDFT or FBM – foot, board measure) is a unit of volume for lumber in the United States and Canada. It represents the volume of a piece of wood that is one foot long, one foot wide, and one inch thick before surfacing. More precisely, it’s 144 cubic inches of wood (12 inches x 12 inches x 1 inch). Knowing how to calculate a board foot is essential for anyone buying, selling, or working with rough-sawn or finished lumber, as it’s the standard unit for pricing and measurement in the hardwood industry and for many softwood applications.
Lumber dealers, woodworkers, carpenters, and construction professionals use board feet to quantify and price lumber. It allows for a standardized way to measure wood regardless of its specific dimensions, focusing instead on its total volume. Understanding how to calculate a board foot ensures you order and pay for the correct amount of material.
Common misconceptions include confusing board feet with linear feet or square feet. Linear feet measure length only, and square feet measure area. A board foot, however, measures volume.
Board Foot Formula and Mathematical Explanation
The formula for calculating board feet depends on the units you use for length:
If Length is in Feet:
Board Feet = (Thickness (inches) × Width (inches) × Length (feet)) / 12
If Length is in Inches:
Board Feet = (Thickness (inches) × Width (inches) × Length (inches)) / 144
The division by 12 or 144 converts the volume from cubic inches (if all dimensions were in inches) into board feet. Since one board foot is 1″ x 12″ x 12″ = 144 cubic inches, we divide the total volume in cubic inches by 144. If the length is already in feet, the formula simplifies to dividing by 12 because the length unit is already feet.
Understanding how to calculate a board foot involves using these simple formulas.
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| T | Thickness | Inches | 0.25 – 6 (nominal) |
| W | Width | Inches | 2 – 16 (nominal) |
| L | Length | Feet or Inches | 2 – 24 feet, or 24 – 288 inches |
| BDFT | Board Feet | Board Feet | 0.1 – 100+ |
Practical Examples (Real-World Use Cases)
Example 1: Calculating Board Feet for a Single Plank
Suppose you have a plank of walnut that is 1.5 inches thick, 8 inches wide, and 10 feet long (nominal dimensions).
- Thickness (T) = 1.5 inches
- Width (W) = 8 inches
- Length (L) = 10 feet
Using the formula (T × W × L) / 12:
Board Feet = (1.5 × 8 × 10) / 12 = 120 / 12 = 10 board feet.
So, that single plank contains 10 board feet of lumber.
Example 2: Calculating Total Board Feet for Multiple Boards
You need to buy 20 pieces of oak lumber, each 2 inches thick, 6 inches wide, and 12 feet long.
- Thickness (T) = 2 inches
- Width (W) = 6 inches
- Length (L) = 12 feet
- Number of pieces = 20
First, calculate board feet for one piece: (2 × 6 × 12) / 12 = 144 / 12 = 12 board feet per piece.
Total Board Feet = 12 board feet/piece × 20 pieces = 240 board feet.
You would need to purchase 240 board feet of oak. Learning how to calculate a board foot for multiple pieces is crucial for larger projects.
How to Use This Board Foot Calculator
Our board foot calculator simplifies the process:
- Enter Thickness: Input the nominal thickness of the lumber in inches.
- Enter Width: Input the nominal width of the lumber in inches.
- Enter Length: Input the length of the lumber.
- Select Length Unit: Choose whether the length you entered is in feet or inches using the dropdown menu.
- Calculate: The calculator automatically updates the board feet as you enter the values, or you can click “Calculate”.
- Read Results: The “Primary Result” shows the board feet for a single piece with the dimensions you entered. “Intermediate Results” show the volume in cubic inches and the dimensions used.
- Reset: Click “Reset” to clear the fields and start over with default values.
- Copy Results: Click “Copy Results” to copy the main result and details to your clipboard.
The chart dynamically updates to show how board feet vary with thickness for the entered width and length, giving you a visual understanding of how to calculate a board foot under different conditions.
Key Factors That Affect Board Foot Results
- Nominal vs. Actual Dimensions: Board feet are typically calculated using *nominal* dimensions (e.g., a 2×4 is nominally 2 inches by 4 inches, but actually smaller after drying and surfacing). Be aware of whether you are using nominal or actual sizes, as pricing is usually based on nominal. Our calculator assumes nominal input.
- Length Unit Consistency: Ensure you select the correct unit (feet or inches) for the length measurement. Using the wrong unit will give drastically different results when learning how to calculate a board foot.
- Rough vs. Surfaced Lumber: Rough-sawn lumber is closer to its nominal dimensions than surfaced lumber (S4S – surfaced four sides). Board foot calculations are generally based on the size before surfacing.
- Waste Factor: When purchasing lumber for a project, always account for waste due to cuts, knots, and defects. You typically buy more board feet than the net volume needed.
- Taper and Irregular Shapes: For logs or irregularly shaped lumber, more complex methods or average dimensions might be needed, and a simple board foot calculator for rectangular boards might not be sufficient.
- Hardwood vs. Softwood Practices: While the board foot is standard, measurement and pricing practices can vary slightly between hardwood and softwood industries, and even regionally.
Frequently Asked Questions (FAQ)
- What is one board foot?
- One board foot is a volume of wood equivalent to 1 inch thick x 12 inches wide x 12 inches long, or 144 cubic inches.
- How do I calculate board feet for multiple pieces?
- Calculate the board feet for one piece using the formula, then multiply by the number of pieces.
- Is board foot calculated on actual or nominal size?
- It is almost always calculated based on the *nominal* size of the lumber, which is the size before final drying and surfacing.
- Why is the divisor 12 or 144?
- If length is in feet, you divide by 12 to convert (T” x W” x L’) into board feet. If length is in inches, you divide (T” x W” x L”) by 144 (12×12) because 1 board foot = 144 cubic inches.
- How do you calculate board feet for a log?
- Calculating board feet in a log is more complex and uses log scaling rules like Doyle, Scribner, or International 1/4″ Rule, which estimate the yield of lumber from the log.
- Does the type of wood affect the board foot calculation?
- No, the board foot is a measure of volume. The type of wood affects the weight and price per board foot, but not the board foot volume itself. The method of how to calculate a board foot remains the same.
- What if my lumber isn’t exactly 1 or 2 inches thick?
- Use the actual or nominal thickness as specified for the calculation. For example, lumber is often sold as 4/4 (four-quarter, nominally 1″), 5/4 (1.25″), 6/4 (1.5″), 8/4 (2″), etc. Use these nominal values.
- How do I convert cubic inches to board feet?
- Divide the total cubic inches by 144 to get board feet.
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Knowing how to calculate a board foot is fundamental for many projects, and these resources can provide further context.