What Is a Board Foot? A Simple Guide for Woodworkers

A stack of freshly cut lumber in a woodworking shop, illustrating the concept of board feet.

A board foot is the most common unit of measurement for lumber volume in the United States and Canada. If you’ve ever felt confused by the term, you’re not alone. Unlike linear feet or square feet, a board foot measures volume, not just length or area.

Understanding this concept is the first step to accurately estimating material needs, budgeting for projects, and communicating effectively with lumber suppliers. This guide breaks down exactly what a board foot is, how to calculate it, and why it matters.

A tape measure lying on a wooden board, ready for measurement.

The Definition: What Exactly Is One Board Foot?

One board foot (BF or bd. ft.) is a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick.

Think of it as a square foot of lumber that is one inch thick. The total volume of one board foot is 144 cubic inches (12″ × 12″ × 1″).

This standardized unit allows buyers and sellers to trade lumber of different shapes and sizes using a consistent volume metric. Whether you’re buying a thick slab or thin boards, the price is often quoted per board foot, giving you a clear way to compare costs.

Quick Facts About Board Feet

It’s a Volume Measurement: Always remember you’re dealing with three dimensions: length, width, and thickness.
Based on Nominal Size: Calculations almost always use the nominal dimensions of the lumber (e.g., a “2x4”), not its smaller actual dimensions.
The Standard for Hardwoods: While construction lumber is often sold by the piece, hardwoods are almost exclusively sold by the board foot.

The Board Foot Formula: How to Calculate It

Calculating board feet is straightforward once you know the formula. There are two common variations depending on whether you measure the length in feet or inches. Both yield the same result.

A hand writing a mathematical formula on a blackboard.

Formula 1: When Length is in Feet

This is the most common formula used in woodworking.

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

Why divide by 12? Because you are converting the length from feet to inches to get a consistent unit before calculating the total cubic inches, and then converting it back to the board foot standard.

Formula 2: When Length is in Inches

This formula is useful if all your measurements are in inches.

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

Why divide by 144? Because one board foot is 144 cubic inches. This formula calculates the total cubic inches of the board and then divides by 144 to find out how many board feet it contains.

Calculation Examples in Action

Let’s apply the formula to some common lumber sizes to see how it works.

A neat stack of 2x4 lumber boards at a construction site.

Example 1: A Standard 2x4x10

Thickness: 2 inches
Width: 4 inches
Length: 10 feet

Using Formula 1: (2" × 4" × 10') / 12 = 80 / 12 = 6.67 Board Feet

So, a 10-foot-long 2x4 contains 6.67 board feet.

Example 2: A 1x6x8 Hardwood Board

Thickness: 1 inch
Width: 6 inches
Length: 8 feet

Using Formula 1: (1" × 6" × 8') / 12 = 48 / 12 = 4.0 Board Feet

Example 3: A 3/4-inch Thick Shelf Board

Let’s say you have a board that is 0.75 inches thick, 8 inches wide, and 48 inches long.

Using Formula 2 (since length is in inches): (0.75" × 8" × 48") / 144 = 288 / 144 = 2.0 Board Feet

Ready to calculate your own? Try our free and accurate Board Foot Calculator to plan your project faster.

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Common Mistakes and Tips for Accuracy

Avoiding a few common pitfalls will ensure your calculations are always accurate.

A thoughtful carpenter looking at a piece of wood, planning the next cut.

Nominal vs. Actual Dimensions: A 2x4 is not actually 2 inches by 4 inches. After milling and drying, its actual size is closer to 1.5” x 3.5”. However, board foot calculations are always based on the nominal dimensions. This is a trade standard, so don’t use the actual measurements unless specifically told to.
Mixing Units: Ensure all your units are consistent before you calculate. If you use the / 12 formula, the length must be in feet. If you use the / 144 formula, the length must be in inches.
Forgetting Waste: The board foot calculation gives you the exact volume of the wood you need. It does not account for waste from cuts (kerf), defects, or mistakes. Always add a waste factor (typically 10-15%) to your final order.

It’s easy to confuse these terms, but they measure different things.

A collage of different wood textures and grains.

Board Foot: Measures Volume (Length × Width × Thickness).
Square Foot: Measures Area (Length × Width). Used for flooring, paneling, etc.
Linear Foot: Measures Length. Used when the width and thickness are standard and irrelevant to the quantity needed (e.g., trim, molding).

To learn more, check out our detailed guide on Board Feet vs. Square Feet vs. Linear Feet.

Frequently Asked Questions (FAQ)

1. What is a board foot in simple terms? A board foot is a chunk of wood that measures 1 foot long, 1 foot wide, and 1 inch thick. It’s a way to measure wood volume.

2. How do you calculate board feet? The easiest way is to multiply the thickness (in), width (in), and length (ft), then divide the total by 12.

3. What is the difference between a board foot and a linear foot? A board foot measures volume, while a linear foot measures only length. You need to know the board’s width and thickness to convert between them.

4. Why are nominal and actual sizes different? Lumber is cut to its nominal size when it’s still green (wet). As it dries, it shrinks, resulting in smaller actual dimensions. The industry standard is to sell based on the original nominal size.

Now that you have a solid understanding of board feet, you’re better equipped to plan your next woodworking project with confidence.