Board Foot Calculator Formula

The board foot calculator works out the volume of lumber in board feet from its dimensions. You enter thickness in inches, width in inches, and length in feet, and it returns the board footage. One board foot equals 1 inch × 12 inches × 1 foot (or 144 cubic inches).

Formula

The standard board foot formula is:

Board Feet = (Thickness (in) × Width (in) × Length (ft)) / 12

Where:

• Thickness is in inches (nominal, not actual).
• Width is in inches (nominal).
• Length is in feet.
• Divide by 12 because one board foot is 1 inch × 12 inches × 1 foot = 144 cubic inches, and the product of thickness and width in inches times length in feet gives cubic inches per foot, which you convert to board feet.

If you measure all three dimensions in inches, the equivalent formula is:

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

Worked Example

Using the default values from the calculator: thickness = 1 in, width = 6 in, length = 8 ft.

1. Multiply thickness by width: 1 × 6 = 6 in².
2. Multiply by length in feet: 6 × 8 = 48 in²·ft.
3. Divide by 12: 48 / 12 = 4 board feet.

The calculator returns 4.00 board feet. The volume in cubic inches is 1 × 6 × (8 × 12) = 576 in³, and in cubic feet it’s 576 / 1728 = 0.333 ft³.

Why Use Board Feet? A Bit of History

Board feet have been used in North America since the 19th century as a standard unit for trading lumber. Before standardized dimensions, buyers and sellers needed a consistent way to price wood regardless of how it was cut. A board that is 1 inch thick, 12 inches wide, and 12 inches long is one board foot, but so is a board 2 inches thick, 6 inches wide, and 12 inches long—same volume, different shape. This unit allows sawmills and lumberyards to quote a single price per unit of volume, making comparisons easier. In most of the world, lumber is sold by the cubic meter, but the U.S. and Canada still use board feet for softwood and hardwood.

Nominal vs. Actual Dimensions: The Most Common Mistake

Lumber is sold by nominal (named) dimensions, not its actual measured size. For example, a “2×4� is actually 1.5 inches by 3.5 inches after planing and drying. When calculating board feet for pricing, you almost always use the nominal dimensions. A 2×4×8 (nominal) is 2 × 4 × 8 / 12 = 5.33 board feet, even though its actual volume is 1.5 × 3.5 × 8 / 12 = 3.5 board feet. If you use actual dimensions for a project, you’ll get a lower volume, which is fine for estimating material, but it will not match what the lumberyard charges. Always confirm whether the price is based on nominal or actual measure—some hardwood dealers use actual (net) measure after surfacing.

How to Measure a Board for Board Feet

For a simple rectangular board, the formula above works directly. But lumber often comes in irregular shapes. Here’s how to handle common cases:

• Multiple boards of the same size: Calculate one board’s footage and multiply by the number of boards.
• Boards with different sizes: Calculate each board separately and add the results.
• Tapered boards (e.g., live-edge slabs): Use the average width (measure at both ends, add, divide by 2) and the longest length.
• Logs: Use the Doyle or Scribner log rules, which estimate board feet from log diameter and length, accounting for saw kerf and waste.

Board Feet vs. Square Feet vs. Cubic Feet

These units are often confused, but they measure different things. Square feet measure area (length × width) and are used for flooring, siding, or sheet goods like plywood. Cubic feet measure volume (length × width × thickness) and are used for concrete or shipping. Board feet are a hybrid: they use thickness in inches, width in inches, and length in feet, giving a volume that is 1/12 of a cubic foot. A 1-inch-thick board that covers 1 square foot is 1 board foot. A 2-inch-thick board covering the same area is 2 board feet. To convert board feet to cubic feet, divide by 12 (since 12 board feet = 1 cubic foot). To convert to cubic meters, multiply board feet by 0.00235974.

Common Mistakes and How to Avoid Them

• Mixing units: Always keep thickness and width in inches, and length in feet. If you measure length in inches, use the /144 formula.
• Using actual instead of nominal dimensions for pricing: Check what the seller uses.
• Forgetting to divide by 12: This is the most frequent error—people multiply and get a number that’s 12 times too large.
• Rounding too early: Round only at the final step to avoid small errors that add up in large orders.
• Confusing board feet with square feet: A 10-foot-long 1×12 is 10 board feet, but it covers 10 square feet—same number only because thickness is 1 inch.

Limits of the Formula

The simple formula assumes a perfectly rectangular, uniform board. Real lumber has defects, warping, and moisture content that affect usable volume. For rough lumber, you measure the rough dimensions before planing. For surfaced lumber, the actual size is smaller, but the nominal size is used for pricing. The formula also doesn’t account for waste from cutting joints, trimming ends, or defects. When estimating for a project, add 10–20% extra for waste. For logs, the formula doesn’t apply directly because logs are round and sawing produces kerf (sawdust) and slabs. Use log rules instead.

Frequently Asked Questions

How many board feet are in a 2×4×8?

Using nominal dimensions: 2 × 4 × 8 / 12 = 5.33 board feet. If you use actual dimensions (1.5 × 3.5 × 8), you get 3.5 board feet. Most lumberyards charge based on nominal dimensions, so expect 5.33.

What is the difference between board foot and linear foot?

A linear foot is simply a length of 12 inches, regardless of width or thickness. A board foot is a volume unit. For example, a 1×6 board that is 10 feet long has 10 linear feet but 5 board feet (1 × 6 × 10 / 12).

How do I convert board feet to cubic feet?

Divide the number of board feet by 12. For instance, 24 board feet = 2 cubic feet. Conversely, multiply cubic feet by 12 to get board feet.

Why do hardwood dealers use board feet but softwood is sold by linear foot?

Hardwoods are typically sold by board foot because they come in random widths and thicknesses, making volume the fairest measure. Softwoods (like dimensional lumber) are often sold by linear foot because they are standardized in size (2×4, 2×6, etc.), so length is the only variable.

Does the formula work for metric measurements?

Not directly. If you measure in centimeters and meters, you can calculate volume in cubic meters and then convert: 1 board foot = 0.00235974 cubic meters. Or convert your dimensions to inches and feet first.

How do I calculate board feet for a log?

You can’t use the simple rectangle formula for a round log. Use a log rule like Doyle or Scribner, which estimates the number of board feet you can saw from a log based on its small-end diameter and length. These rules are tables or formulas that account for saw kerf and waste.

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in t | Thickness | in | 1 | 0
in w | Width | in | 6 | 0
in l | Length | ft | 8 | 0
out bdft | Board feet | bd ft | (t * w * l) / 12 | 2
out cu_in | Volume | in³ | t * w * (l * 12) | 0
out cu_ft | Volume | ft³ | (t * w * (l * 12)) / 1728 | 3