How To Calculate A Board Foot

Understand and calculate the board feet of your lumber quickly.

Board Feet per Linear Foot for Common Lumber Sizes

Nominal Size (in)	Actual Size (in)	Board Feet per Foot
1×4	0.75 x 3.5	0.29
1×6	0.75 x 5.5	0.46
1×8	0.75 x 7.25	0.60
1×12	0.75 x 11.25	0.94
2×4	1.5 x 3.5	0.58
2×6	1.5 x 5.5	0.92
2×8	1.5 x 7.25	1.21
2×10	1.5 x 9.25	1.54
2×12	1.5 x 11.25	1.88
4×4	3.5 x 3.5	1.36

What is a Board Foot? (and how to calculate a board foot)

A board foot (BF or bd. ft.) is a unit of volume measurement 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 (1 inch) thick, or its equivalent. So, one board foot is equal to 144 cubic inches (12″ x 12″ x 1″). Understanding how to calculate a board foot is crucial for anyone working with lumber, from hobbyist woodworkers to professional contractors and lumber suppliers.

Anyone buying, selling, or estimating lumber for projects needs to know how to calculate a board foot. This includes carpenters, furniture makers, builders, and even DIY enthusiasts. It’s the standard unit for pricing and selling many types of lumber, especially hardwoods.

A common misconception is that board feet relate directly to the linear feet of a board without considering its thickness and width. However, how to calculate a board foot always involves all three dimensions: thickness, width, and length.

Board Foot Formula and Mathematical Explanation

The formula for how to calculate a board foot depends on the units you use for the dimensions:

• If length is measured in feet:
  Board Feet (BF) = (Thickness (inches) × Width (inches) × Length (feet)) / 12
• If length is measured in inches:
  Board Feet (BF) = (Thickness (inches) × Width (inches) × Length (inches)) / 144

The division by 12 or 144 is necessary to convert the volume from units involving inches and feet (or just inches) into the standard board foot unit, which is equivalent to 144 cubic inches.

Here’s a step-by-step derivation for the length in feet formula:

1. Volume in cubic inches = Thickness (in) × Width (in) × Length (in)
2. Since 1 foot = 12 inches, Length (in) = Length (ft) × 12
3. Volume in cubic inches = Thickness (in) × Width (in) × (Length (ft) × 12)
4. One board foot = 144 cubic inches.
5. Number of board feet = Volume in cubic inches / 144
6. Board Feet = (Thickness (in) × Width (in) × Length (ft) × 12) / 144
7. Board Feet = (Thickness (in) × Width (in) × Length (ft)) / 12

Variables Table

Variable	Meaning	Unit	Typical Range
T	Thickness of lumber	inches	0.25 – 12 (nominal)
W	Width of lumber	inches	1 – 24 (nominal)
L	Length of lumber	feet or inches	1 – 24 (feet)
BF	Board Feet	Board Foot	0.1 – 100+

Practical Examples (Real-World Use Cases of calculating board foot)

Understanding how to calculate a board foot is best illustrated with examples.

Example 1: Buying Hardwood

You need to buy some oak boards that are 1 inch thick, 6 inches wide, and 8 feet long. You need 5 such boards.

• Thickness = 1 inch
• Width = 6 inches
• Length = 8 feet
• Quantity = 5

Board Feet per board = (1″ × 6″ × 8′) / 12 = 48 / 12 = 4 BF

Total Board Feet = 4 BF/board × 5 boards = 20 BF

If the oak costs $7 per board foot, the total cost would be 20 BF × $7/BF = $140.

Example 2: Estimating Lumber for a Deck

You are building a small deck and need 2×6 lumber (which is actually 1.5″ x 5.5″) for the joists. You need ten joists, each 10 feet long.

• Thickness = 1.5 inches (actual)
• Width = 5.5 inches (actual)
• Length = 10 feet
• Quantity = 10

Board Feet per joist = (1.5″ × 5.5″ × 10′) / 12 = 82.5 / 12 = 6.875 BF

Total Board Feet = 6.875 BF/joist × 10 joists = 68.75 BF

Knowing how to calculate a board foot helps you accurately estimate material costs.

How to Use This Board Foot Calculator

Our calculator makes it easy to figure out how to calculate a board foot:

1. Enter Thickness: Input the nominal thickness of your lumber in inches.
2. Enter Width: Input the nominal width of your lumber in inches.
3. Enter Length and Unit: Input the length and select whether it’s in feet or inches from the dropdown.
4. Enter Quantity: Specify how many pieces of lumber you have with these dimensions.
5. View Results: The calculator instantly shows the Total Board Feet, Board Feet per Piece, and volume in cubic inches and cubic feet. The formula used is also displayed.
6. Reset: Use the “Reset” button to clear inputs to default values.
7. Copy: Use the “Copy Results” button to copy the inputs and results to your clipboard.

The results help you understand the volume of lumber you’re working with, crucial for purchasing and pricing. The chart also visualizes how board feet change with length for the entered dimensions, giving a quick visual comparison.

Key Factors That Affect Board Foot Calculation

Several factors are important when learning how to calculate a board foot and working with lumber:

1. Nominal vs. Actual Dimensions: Lumber is often sold using “nominal” dimensions (like 2×4), but the “actual” dressed dimensions are smaller (like 1.5″ x 3.5″). Board foot calculations are usually based on nominal dimensions before drying and surfacing, but it’s crucial to clarify with the supplier whether they are pricing based on nominal or actual size when calculating board feet. Our calculator assumes nominal input, but be aware of the difference.
2. Length Unit: Ensure you select the correct unit (feet or inches) for the length measurement, as it changes the divisor in the formula (12 for feet, 144 for inches).
3. Thickness: The thickness in inches directly impacts the board foot volume.
4. Width: The width in inches is another direct factor in the volume calculation.
5. Quantity: The total board feet scale linearly with the number of pieces.
6. Waste Factor: When purchasing lumber, always add a waste factor (e.g., 10-15%) to your total board feet calculation to account for cuts, knots, and defects. Our {related_keywords[0]} might help estimate this.

Frequently Asked Questions (FAQ) about how to calculate a board foot

1. What is one board foot?

One board foot is a volume of lumber equivalent to 1 inch thick x 12 inches wide x 12 inches long (144 cubic inches).

2. How do I calculate board feet for lumber with fractional thickness?

Use the fractional thickness in the formula. For example, for 5/4″ thick lumber, use 1.25 inches as the thickness when you calculate board foot.

3. Why is the divisor 12 or 144 when calculating board foot?

If length is in feet, you divide by 12 to convert the product of inches x inches x feet to board feet. If length is in inches, you divide by 144 (12×12) because 1 board foot = 144 cubic inches.

4. Is board foot calculation based on nominal or actual size?

Traditionally, for hardwoods and rough-sawn lumber, it’s based on nominal sizes before final milling. For surfaced softwood (like 2x4s), it’s still often referenced by nominal size even though the actual is smaller. Always clarify with your supplier.

5. How to calculate board foot for a round log?

Calculating board feet from a log is more complex and involves log scaling rules like Doyle, Scribner, or International 1/4″ rule, which estimate the yield of sawn lumber. Our calculator is for sawn lumber, not logs.

6. Does the type of wood affect how to calculate a board foot?

No, the board foot is a measure of volume, independent of wood type. However, the price per board foot varies greatly between wood species. Check out our guide on {related_keywords[1]} for more info.

7. How many board feet are in a 2×4 that is 8 feet long?

Using nominal dimensions: (2″ × 4″ × 8′) / 12 = 64 / 12 = 5.33 BF. Using actual (1.5″ x 3.5″): (1.5″ x 3.5″ x 8′) / 12 = 42 / 12 = 3.5 BF. Pricing is usually based on nominal for 2x4s.

8. Where can I find more about {related_keywords[2]}?

Industry standards often define how measurements are taken and board feet are calculated, especially for different grades and types of lumber.

Related Tools and Internal Resources

• {related_keywords[0]}: Calculate the total volume of lumber needed, including waste.
• {related_keywords[1]}: A basic guide to measuring wood for various projects.
• {related_keywords[2]}: Learn about industry standards for timber and lumber.
• {related_keywords[3]}: Understand how hardwood is priced by the board foot for projects like flooring.
• {related_keywords[4]}: Tips and tricks for various woodworking endeavors where board foot calculations are essential.
• {related_keywords[5]}: A guide to buying lumber effectively from a lumber yard, understanding board feet and pricing.