How To Calculate A Board Foot

Accurately determine the board feet of your lumber with our easy-to-use calculator. Understanding how to calculate a board foot is essential for woodworkers and builders.

Board Foot Calculator

What is a Board Foot?

A board foot (FBM – 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 (12 inches) long, one foot (12 inches) wide, and one inch thick, or its equivalent. So, one board foot is equal to 144 cubic inches (12″ x 12″ x 1″). Learning how to calculate a board foot is crucial for accurately estimating lumber quantities and costs for woodworking, construction, and other projects.

Anyone buying, selling, or working with rough-sawn or finished lumber should know how to calculate a board foot. This includes woodworkers, carpenters, contractors, lumberyard staff, and hobbyists. It’s the standard unit for pricing most hardwood lumber and some softwoods, especially in rough form.

A common misconception is that a board foot is a measure of length or area. It is strictly a measure of volume. Another point of confusion arises with nominal vs. actual dimensions, which we’ll discuss later. When you calculate board foot measurements, you are quantifying the volume of wood.

Board Foot Formula and Mathematical Explanation

The standard formula to calculate a board foot is:

Board Feet = (Thickness (inches) × Width (inches) × Length (feet)) / 12

Alternatively, if all dimensions are in inches:

Board Feet = (Thickness (inches) × Width (inches) × Length (inches)) / 144

Step-by-step derivation using the first formula:

1. Measure the thickness of the lumber in inches.
2. Measure the width of the lumber in inches.
3. Measure the length of the lumber in feet.
4. Multiply these three dimensions together: Thickness (in) × Width (in) × Length (ft). This gives you a volume unit that is inches x inches x feet.
5. To convert this to board feet (which is based on 144 cubic inches or 1 ft x 1 ft x 1 inch), we divide by 12 (because 1 foot = 12 inches, and the length is already in feet, so we are converting the width from inches to feet effectively in the volume context relative to the thickness unit).

When you calculate board foot values, you are essentially finding out how many 12″x12″x1″ blocks of wood are contained within your piece of lumber.

Variables Table

Variable	Meaning	Unit	Typical Range
T	Thickness of the lumber	inches	0.25 – 4+
W	Width of the lumber	inches	1 – 12+
L (ft)	Length of the lumber	feet	1 – 20+
L (in)	Length of the lumber	inches	12 – 240+
BF	Board Feet	Board Feet	0.1 – 50+

Variables used in the board foot calculation.

Practical Examples (Real-World Use Cases)

Example 1: Calculating Board Feet for a Hardwood Plank

Suppose you have a piece of rough-sawn cherry that is 1.5 inches thick, 8 inches wide, and 10 feet long.

• Thickness (T) = 1.5 inches
• Width (W) = 8 inches
• Length (L) = 10 feet

Board Feet = (1.5 × 8 × 10) / 12 = 120 / 12 = 10 Board Feet.

So, this plank contains 10 board feet of wood. If the cherry costs $7 per board foot, the plank would cost 10 * $7 = $70.

Example 2: Calculating Board Feet for Multiple Boards

You need to buy five 2×4 boards, each 8 feet long, for a framing project. A nominal 2×4 is actually 1.5 inches thick by 3.5 inches wide.

• Thickness (T) = 1.5 inches
• Width (W) = 3.5 inches
• Length (L) = 8 feet

Board Feet per board = (1.5 × 3.5 × 8) / 12 = 42 / 12 = 3.5 Board Feet.

For five boards, the total is 5 × 3.5 = 17.5 Board Feet. Knowing how to calculate a board foot helps you order the correct total volume.

How to Use This Board Foot Calculator

Our calculator makes it easy to calculate board foot volume:

1. Enter Thickness: Input the thickness of your lumber in inches into the “Thickness (T, inches)” field. Use actual dimensions if known, especially for hardwoods.
2. Enter Width: Input the width of your lumber in inches into the “Width (W, inches)” field. Again, use actual dimensions where possible.
3. Enter Length: Input the length of your lumber in feet into the “Length (L, feet)” field.
4. View Results: The calculator will instantly display the total board feet in the “Primary Result” area, along with the volume in cubic inches.
5. Reset: Click the “Reset” button to clear the fields and start over with default values.
6. Copy Results: Click “Copy Results” to copy the main result and intermediate values to your clipboard.

The results show the volume of wood in board feet. This is the figure you’d typically use when purchasing or selling lumber by volume, especially hardwoods.

Key Factors That Affect Board Foot Calculations

• Nominal vs. Actual Dimensions: Softwood lumber (like 2x4s) is sold using nominal dimensions, but their actual dimensions are smaller after drying and planing. For example, a 2×4 is actually 1.5″ x 3.5″. Hardwoods are often sold by their actual dimensions when rough, or after surfacing. Always clarify whether nominal or actual dimensions are being used, as it significantly impacts the board foot calculation. Our nominal vs actual lumber guide explains more.
• Rough vs. Surfaced Lumber: Rough lumber is not planed smooth and is closer to its full nominal or rough-sawn dimension. Surfaced lumber (S2S – surfaced two sides, S4S – surfaced four sides) is thinner and narrower. The board foot calculation should ideally use the dimensions before surfacing if buying rough, or actual after surfacing.
• Taper and Irregular Shapes: The standard formula assumes rectangular boards. For tapered or irregularly shaped boards, you might average the width or use more complex volume calculations and then convert to board feet.
• Waste Factor: When planning projects, add a waste factor (e.g., 10-20%) to your total board footage to account for cuts, defects, and unusable parts. Our woodworking waste calculator can help.
• Kerf Width: The width of the saw blade (kerf) removes material with each cut, which can add up over many cuts, effectively reducing your usable volume compared to the initial board foot calculation.
• Length Measurement: Ensure length is measured accurately in feet or converted correctly from inches (12 inches = 1 foot) for the primary formula.

Common Nominal vs. Actual Lumber Dimensions and Board Feet (for 8 ft length)

This table shows common softwood lumber sizes, their actual dimensions after surfacing, and the board feet for an 8-foot length using actual dimensions.

Nominal Size (in)	Actual Thickness (in)	Actual Width (in)	Board Feet (8 ft length)
1×2	0.75	1.5	0.75
1×4	0.75	3.5	1.75
1×6	0.75	5.5	2.75
1×8	0.75	7.25	3.63
2×4	1.5	3.5	3.50
2×6	1.5	5.5	5.50
2×8	1.5	7.25	7.25
2×10	1.5	9.25	9.25
2×12	1.5	11.25	11.25
4×4	3.5	3.5	8.17

Board feet for standard 8-foot lumber using actual dimensions.

Frequently Asked Questions (FAQ)

Q: What is the difference between a board foot and a linear foot?

A: A board foot is a measure of volume (144 cubic inches), while a linear foot is simply a measure of length (12 inches), regardless of thickness or width. Lumber like molding or trim is often sold by the linear foot. Use our board foot to linear foot converter for more.

Q: How do I calculate board feet for lumber sold by nominal dimensions?

A: For softwoods sold by nominal size, it’s common practice to calculate board feet using the nominal dimensions, even though the actual wood volume is less. However, for hardwoods, board feet are almost always calculated based on actual (or rough sawn) dimensions after kiln drying but before final surfacing for retail. Always clarify with the seller.

Q: Why is the denominator 12 in the board foot formula?

A: The denominator is 12 when your length is in feet, and thickness and width are in inches. It converts the ft unit of length to inches to be consistent with a board foot being 1″ thick x 12″ wide x 12″ long (144 cu in), but since we use length in feet, we divide by 12 (1 ft = 12 in). If all dimensions were in inches, you would divide by 144.

Q: How do I calculate board feet for a round log?

A: Calculating the board feet yield from a log is more complex and uses log scaling rules like Doyle, Scribner, or International 1/4″ rule, which estimate the amount of sawn lumber a log can produce. This calculator is for sawn lumber.

Q: Do I need to account for the saw blade width (kerf) when calculating board feet for a project?

A: When estimating the total lumber needed for a project with many cuts, yes, you should add extra material (waste factor) to account for kerf losses and other waste. The board foot calculation itself doesn’t include kerf.

Q: How many board feet are in a 2×4 that is 8 feet long?

A: Using actual dimensions (1.5″ x 3.5″ x 8′): (1.5 * 3.5 * 8) / 12 = 3.5 board feet. Using nominal (2″ x 4″ x 8′): (2 * 4 * 8) / 12 = 5.33 board feet. Softwood is often referred to by nominal when calculating BF for simplicity, but you get less wood.

Q: How is the price of lumber related to board feet?

A: Hardwood lumber is typically priced per board foot. To find the cost of a board, you calculate the board foot volume and multiply by the price per board foot. For instance, 5 BF of walnut at $9/BF would be $45. Our lumber cost estimator can help.

Q: Can I use this calculator for plywood or sheet goods?

A: No, plywood and sheet goods are typically sold by the square foot (area) for a given thickness, not by the board foot. This calculator is for solid lumber.

Related Tools and Internal Resources

• Lumber Types Guide: Learn about different types of wood and their uses.
• Woodworking Project Ideas: Get inspiration for your next project.
• Construction Materials Calculator: Estimate materials for various construction projects.
• Board Foot to Linear Foot Converter: Convert between volume and length for specific dimensions.
• Woodworking Waste Calculator: Estimate how much extra wood to buy.
• Lumber Cost Estimator: Calculate the cost of lumber based on board feet and price.