Board Foot (Bd Ft) Calculator
Easily calculate board feet for your lumber projects. Understand how do you calculate bd ft with our simple tool and detailed guide.
Calculate Board Feet
Board Feet vs. Length (for given T & W)
Bd Ft (Varying Length)
Board Feet at Different Dimensions
| Length (ft) | Width (in) | Thickness (in) | Board Feet/Piece |
|---|---|---|---|
| Enter values and calculate to see table. | |||
What is Board Feet (Bd Ft)?
A board foot (often abbreviated as Bd Ft, FBM for foot board measure, or BF) 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, or its equivalent. Understanding how do you calculate bd ft is crucial for anyone buying, selling, or working with lumber, especially hardwoods, which are often sold by the board foot.
One board foot is equal to 144 cubic inches (1 ft x 1 ft x 1 in = 12 in x 12 in x 1 in = 144 cu in).
Woodworkers, lumber suppliers, contractors, and hobbyists use board foot measurements to estimate the amount of lumber needed for a project and to calculate its cost. It’s a standard measure that allows for consistent pricing and ordering, regardless of the specific dimensions of individual boards, as long as the total volume is known.
Common Misconceptions
- Board feet vs. Linear feet: Linear feet measure only length, while board feet measure volume. A 1×6 board 8 feet long is 8 linear feet, but its board footage is different.
- Nominal vs. Actual Dimensions: Board feet are often calculated based on the *nominal* dimensions (e.g., a “2×4″) before the wood is dried and surfaced, not the smaller *actual* dimensions (e.g., 1.5″ x 3.5”). Our calculator uses the dimensions you enter, so be aware if you are using nominal or actual.
Board Feet Formula and Mathematical Explanation
The formula to calculate board feet depends on the units you use for length:
When Length is in Feet:
Board Feet (Bd Ft) = (Thickness (inches) × Width (inches) × Length (feet)) / 12
When Length is in Inches:
Board Feet (Bd Ft) = (Thickness (inches) × Width (inches) × Length (inches)) / 144
Both formulas give the same result because there are 12 inches in a foot, so dividing by 144 (12×12) for length in inches is equivalent to dividing by 12 for length in feet.
Step-by-Step Calculation:
- Measure the thickness of the lumber in inches.
- Measure the width of the lumber in inches.
- Measure the length of the lumber either in feet or inches.
- Multiply the thickness, width, and length.
- If the length was in feet, divide the result by 12. If the length was in inches, divide by 144.
- The result is the board footage for one piece of lumber. Multiply by the number of pieces for the total.
Variables Table:
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| T | Thickness | Inches | 0.25 – 4 (actual) |
| W | Width | Inches | 1.5 – 12 (actual) |
| L (feet) | Length | Feet | 1 – 20 |
| L (inches) | Length | Inches | 12 – 240 |
| Bd Ft | Board Feet | Bd Ft | 0.1 – 100+ per piece |
Practical Examples (Real-World Use Cases)
Example 1: Buying Hardwood for a Tabletop
You need to buy rough-sawn maple for a tabletop. The boards you find are 1.5 inches thick (6/4), 8 inches wide, and 10 feet long. You need 3 such boards.
- Thickness (T) = 1.5 inches
- Width (W) = 8 inches
- Length (L) = 10 feet
- Number of Pieces = 3
Bd Ft per piece = (1.5 * 8 * 10) / 12 = 120 / 12 = 10 Bd Ft
Total Bd Ft = 10 Bd Ft/piece * 3 pieces = 30 Bd Ft
If the maple costs $7 per board foot, the total cost would be 30 * $7 = $210 (before tax and waste).
Example 2: Calculating Board Feet for Decking
You are building a deck using boards that are actually 1 inch thick, 5.5 inches wide, and 12 feet long. You need 50 boards.
- Thickness (T) = 1 inch
- Width (W) = 5.5 inches
- Length (L) = 12 feet
- Number of Pieces = 50
Bd Ft per piece = (1 * 5.5 * 12) / 12 = 66 / 12 = 5.5 Bd Ft
Total Bd Ft = 5.5 Bd Ft/piece * 50 pieces = 275 Bd Ft
Knowing how to calculate board feet helps you compare prices and ensure you order enough material.
How to Use This Board Foot Calculator
- Enter Thickness: Input the thickness of your lumber in inches into the “Thickness (T, inches)” field.
- Enter Width: Input the width of your lumber in inches into the “Width (W, inches)” field.
- Enter Length: Input the length of your lumber into the “Length (L)” field.
- Select Length Unit: Choose whether the length you entered is in “Feet” or “Inches” from the dropdown menu.
- Enter Number of Pieces: Input the quantity of identical lumber pieces you have or need.
- Calculate: The calculator will automatically update the results as you input the values. You can also click the “Calculate” button.
- View Results: The “Total Board Feet” is displayed prominently, along with “Board Feet per Piece,” “Volume per Piece (cubic inches),” and “Volume per Piece (cubic feet).”
- Use Table & Chart: The table and chart below the calculator show how board footage changes with different dimensions around your inputs, giving you a broader perspective.
- Reset: Click “Reset” to clear the fields to default values.
- Copy Results: Click “Copy Results” to copy the main outputs to your clipboard.
Understanding the results helps you estimate material costs, plan your woodworking projects, and communicate effectively with lumber suppliers.
Key Factors That Affect Board Feet Calculation Results
- Accuracy of Measurements: Small errors in measuring thickness, width, or length can lead to significant differences in the calculated board feet, especially with many pieces. Always measure carefully.
- Nominal vs. Actual Dimensions: Be clear whether you are using nominal (e.g., 2×4) or actual (e.g., 1.5″ x 3.5″) dimensions. Hardwoods are often sold based on thickness before final milling (e.g., 4/4, 5/4, 6/4, 8/4 referring to quarters of an inch). Softwoods are typically sold based on nominal sizes, but board footage might be calculated on actual or nominal depending on the supplier and context. To calculate board feet accurately for cost, know which dimension is being used.
- Rough vs. Surfaced Lumber: Rough-sawn lumber is thicker and wider than surfaced lumber (S2S, S4S). Board footage calculations should ideally use the dimensions at the point of sale/measurement.
- Tapering and Irregular Shapes: For boards that are not uniformly wide or thick, you may need to average the dimensions or use more complex methods to get an accurate board foot measure. The standard formula assumes rectangular boards.
- Waste Factor: When purchasing lumber, always add a waste factor (e.g., 10-20% extra board footage) to account for cuts, knots, and defects. Our waste allowance guide can help.
- Lumber Grade and Defects: While not affecting the volume calculation directly, the grade and presence of defects influence how much *usable* wood you get from a given board footage.
Frequently Asked Questions (FAQ)
- Q1: What does “4/4” or “8/4” mean for lumber thickness?
- A1: This notation refers to the thickness of rough-sawn hardwood in quarters of an inch. 4/4 (four-quarter) is approximately 1 inch thick, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches thick before surfacing.
- Q2: How do you calculate board feet for a log?
- A2: Calculating board feet from a log is more complex and uses log scaling rules like Doyle, Scribner, or International 1/4″ Rule, which estimate the yield of lumber after milling, considering taper and saw kerf.
- Q3: Is board footage the same as square footage?
- A3: No. Square footage measures area (length x width), while board footage measures volume (length x width x thickness / 12 or 144).
- Q4: Why is the denominator 12 or 144 in the board foot formula?
- A4: If length is in feet, you divide by 12 to convert the 1-inch thickness to feet (1 inch = 1/12 foot), making all dimensions effectively in feet before multiplying, then adjust. More simply, 1 board foot = 12″ x 12″ x 1″ = 144 cubic inches. If all dimensions are in inches, divide by 144. If length is in feet, it’s (T” x W” x L’ * 12″) / 144 = (T” x W” x L’) / 12.
- Q5: Does the type of wood affect the board foot calculation?
- A5: No, the board foot calculation is purely a volume measurement based on dimensions. However, the density and weight will vary between lumber types with the same board footage.
- Q6: How do I account for saw kerf (the wood removed by the saw blade)?
- A6: When re-sawing lumber, the saw kerf reduces the yield. The initial board foot calculation is based on the starting dimensions. If you plan to re-saw, you’ll get less total thickness from the resulting pieces.
- Q7: What is FBM?
- A7: FBM stands for “Foot Board Measure,” which is another term for board feet.
- Q8: When buying lumber, are prices always per board foot?
- A8: Hardwoods are very commonly priced per board foot. Softwoods are often priced per linear foot or per piece, especially dimensional lumber, but the price is derived from the board footage or a similar volume/size measure.
Related Tools and Internal Resources
- Woodworking Projects Planner: Plan your material needs for various projects.
- Guide to Lumber Types: Learn about different wood species and their properties.
- Wood Density and Weight Calculator: Estimate the weight of your lumber based on board footage and species.
- Lumber Waste Allowance Guide: Understand how much extra material to order.
- Choosing Hardwoods vs Softwoods: Compare different wood types for your needs.
- Project Cost Estimator: Estimate the total cost of your lumber and other materials.