If you’ve ever wandered the aisles of a lumberyard, you’ve probably seen prices listed by the “board foot” and wondered what it really means. Maybe you’re a seasoned woodworker planning your next project, or perhaps you’re just a DIY enthusiast trying to make sense of a stack of planks at the hardware store. Wherever you land on the experience spectrum, understanding how to calculate board feet is an essential skill that can save you money, prevent waste, and ensure you walk away with just the right amount of wood every time.
Calculating board feet isn’t rocket science, but it’s a topic that often stumps both beginners and even some pros. In this article, we’ll break down everything you need to know: what board feet are, why the measurement matters, the simple formula (and a few shortcuts), how thickness, width, and length factor in, and how to handle odd-shaped or irregular lumber. We’ll also cover common mistakes, practical examples, and answer the most frequently asked questions about board feet. By the end of this article, you’ll feel confident walking into any lumberyard, calculator (or smartphone!) in hand, ready to buy exactly what you need.
What Is a Board Foot, Anyway?
Before you can calculate board feet, you need to know what a board foot actually is.
A board foot is a unit of measurement for lumber volume. It’s used primarily in North America to measure hardwoods, some softwoods, and specialty woods. One board foot is equal to a piece of wood that’s 1 inch thick, 12 inches wide, and 12 inches long.
Board Foot in Numbers
- 1 board foot = 1” thick x 12” wide x 12” long
- 1 board foot = 144 cubic inches of wood
- Board feet (often abbreviated as “BF” or “bd. ft.”) are used to give you a sense of the actual volume of lumber, not just its length or width.
You might see lumber sold by the linear foot, square foot, or board foot. Each serves a different purpose, but when you’re buying dimensional lumber and need to know how much actual wood you’re getting (and paying for), the board foot is king.
Why Use Board Feet?
Board feet are helpful because they standardize wood measurement, regardless of the board’s actual size. If you and a friend both buy 10 board feet of lumber, you’ll both get the same volume, even if one piece is thick and short and the other is thin and long.
Lumberyards price hardwoods and many specialty woods by the board foot. Understanding the calculation means you can estimate costs accurately, compare prices, and avoid being overcharged or buying more than you need.
The Simple Formula for Calculating Board Feet
Let’s cut to the chase: How do you actually calculate board feet?
The Board Foot Formula
The standard formula for board feet is:
Board Feet = (Thickness [in inches] x Width [in inches] x Length [in inches]) / 144
Where:
- Thickness = the thickness of the board in inches (often written as “T”)
- Width = the width of the board in inches (“W”)
- Length = the length of the board in inches (“L”)
- 144 = the number of cubic inches in one board foot (12 x 12 x 1)
Example:
You have a board that’s 2 inches thick, 6 inches wide, and 96 inches long.
Board Feet = (2 x 6 x 96) / 144
Board Feet = (1,152) / 144
Board Feet = 8
So, this board contains 8 board feet.
Why Divide by 144?
Because one board foot is 144 cubic inches (12 x 12 x 1). By dividing your total cubic inches by 144, you’re converting the total volume to board feet.
Quick Reference Formula
If your measurements are already in inches, use the standard formula above.
But what if your measurements are in feet? Here’s a handy shortcut:
Board Feet = Thickness (in inches) x Width (in inches) x Length (in feet) / 12
Or, if all dimensions are in feet:
Board Feet = Thickness (in feet) x Width (in feet) x Length (in feet) x 12
But since lumber is almost always measured in inches for thickness and width, and feet for length, the first formula is most common.
Board Feet Calculator on the Go
Nowadays, you don’t even need to do the math by hand. There are dozens of free board foot calculators online and as mobile apps. Just plug in your numbers and get an instant answer. However, knowing the math behind the tool gives you a huge advantage—especially if you’re double-checking someone else’s calculations or working where cell service is spotty!
Common Lumber Sizes: How Thickness, Width, and Length Factor In
In practice, most lumber you’ll buy is sold in certain “standard” thicknesses—such as 4/4, 5/4, 6/4, 8/4, and so on. Here’s what those mean:
- 4/4 (“four-quarter”) = 1 inch thick
- 5/4 (“five-quarter”) = 1.25 inches thick
- 6/4 (“six-quarter”) = 1.5 inches thick
- 8/4 (“eight-quarter”) = 2 inches thick
Keep in mind that these are nominal thicknesses; the actual measurement after surfacing or planing may be slightly less.
Widths and lengths vary, especially with hardwood lumber. You’ll often see boards labeled by their thickness and random width and length. For softwoods, widths and lengths are usually standardized (such as 2x4s, 2x6s, etc.), but the board foot calculation is the same.
Example With Standard Lumber
Suppose you buy a 2×8 that’s 10 feet long:
- Thickness: 2 inches
- Width: 8 inches
- Length: 10 feet = 120 inches
Board Feet = (2 x 8 x 120) / 144
Board Feet = (1,920) / 144
Board Feet ≈ 13.33
This board contains about 13.33 board feet.
Calculating Board Feet for Multiple Boards
Rarely do you buy just one board. More often, you’re buying several of the same size. Here’s how to handle it:
Board Feet (total) = Board Feet (single board) x Number of Boards
Or, for identical boards:
Board Feet = (Thickness x Width x Length x Quantity) / 144
Example
You need 5 boards, each 1.5” x 6” x 72”:
Board Feet = (1.5 x 6 x 72 x 5) / 144
Board Feet = (1.5 x 6 x 72) = 648
648 x 5 = 3,240
3,240 / 144 = 22.5
So, you need 22.5 board feet for your project.
Dealing With Odd-Shaped or Irregular Boards
Not all boards are perfect rectangles. Sometimes you’ll work with rough-cut, live-edge, or irregular lumber.
How to Measure Irregular Boards
The standard approach:
- Measure width at the narrowest point
- Use the shortest length
- Measure the actual thickness at its thinnest point
This method ensures you’re not overestimating the usable wood.
Tip: For slabs or live-edge lumber, take several width measurements along the length, average them, and use that as your width. Always err on the side of caution to avoid overestimating the board feet.
Why Board Feet Matter for Pricing and Planning
Pricing Lumber
Most hardwood lumber is priced per board foot. Understanding how to calculate board feet allows you to:
- Accurately estimate costs
- Compare prices between suppliers
- Avoid being overcharged
Example: If cherry costs $7.50 per board foot, and you need 20 board feet, your lumber cost is $150.
Planning Projects
If you’re building a dining table, you need to know not just the dimensions, but also how much wood to buy to allow for mistakes, waste, and grain matching. Calculating board feet helps you:
- Buy enough material (without too much excess)
- Estimate project costs more accurately
- Minimize waste during cutting and milling
Communicating With Suppliers
Suppliers often ask, “How many board feet do you need?” If you can answer confidently, you’ll be taken seriously and reduce confusion.
Common Mistakes in Calculating Board Feet
Even seasoned woodworkers occasionally make mistakes when calculating board feet. Here are the most common pitfalls—and how to avoid them.
1. Mixing Units
Always use inches for thickness and width, and inches or feet for length (but convert consistently). Mixing inches and feet without converting is the #1 error.
2. Using Nominal Instead of Actual Size
Remember, a “2×4” is not actually 2” x 4”. After surfacing, it’s generally 1.5” x 3.5”. Use the actual, measured size for calculations.
3. Forgetting to Account for Waste
When planning a project, always buy a little extra (usually 10-20%) to account for knots, defects, and errors.
4. Not Measuring at the Narrowest/Shortest Point
Especially with rough or live-edge lumber, use the smallest usable measurements.
5. Ignoring Thickness Conversions
If you’re working with metric lumber or thickness in millimeters, convert to inches before using the formula.
Real-World Examples: Calculating Board Feet for Projects
Let’s put the theory into practice with some real-life scenarios.
Example 1: Building a Bookshelf
You want to build a bookshelf that requires the following boards:
- 2 shelves: 3/4” thick x 10” wide x 36” long
- 2 sides: 3/4” thick x 12” wide x 60” long
- 1 top: 3/4” thick x 10” wide x 36” long
Calculate the board feet for each piece:
Shelves:
(0.75 x 10 x 36) / 144 = 1.875 BF per shelf
1.875 x 2 = 3.75 BF
Sides:
(0.75 x 12 x 60) / 144 = 3.75 BF per side
3.75 x 2 = 7.5 BF
Top:
(0.75 x 10 x 36) / 144 = 1.875 BF
Total Board Feet:
3.75 + 7.5 + 1.875 = 13.125 BF
Add 10% for waste: 13.125 x 1.10 ≈ 14.44 BF
So, you’ll need about 14.5 board feet of lumber for your bookshelf.
Example 2: Decking Project
Suppose you’re building a small deck and need to calculate the board feet for 15 boards, each 2” x 6” x 12’.
- Thickness: 2”
- Width: 6”
- Length: 12’ = 144”
Board Feet per board = (2 x 6 x 144) / 144 = 12 BF
Total = 12 BF x 15 = 180 BF
Pro Tips for Accurate Board Foot Calculations
- Always double-check your math—especially when working with expensive woods.
- Use a calculator or app for quick, reliable results on the job site.
- Bring a tape measure and measure boards yourself; don’t rely on nominal dimensions.
- Add waste factor—better to have a little left over than come up short.
- Record your calculations so you can reference them if there’s a discrepancy at the lumberyard.
Using Technology: Board Foot Calculators and Apps
You don’t have to do the math in your head. There are great board feet calculators available online and as smartphone apps. Some even allow you to:
- Input a list of boards and get a total instantly
- Switch between metric and imperial units
- Save calculations for different projects
- Estimate costs based on current lumber prices
Before you buy lumber for your next project, try using one of these calculators. They’re especially helpful on the go, in the shop, or when ordering wood online.
Conclusion: Board Feet—A Woodworker’s Best Friend
Knowing how to calculate board feet is a core skill for anyone who works with wood. Whether you’re building a bookshelf, designing custom furniture, framing a house, or tackling a backyard deck, this simple formula ensures you get the right amount of lumber—no more, no less.
Remember:
Board Feet = (Thickness [in inches] x Width [in inches] x Length [in inches]) / 144
It’s that simple. With a bit of practice, you’ll find yourself estimating board feet by sight, impressing your friends at the lumberyard, and saving both time and money on every project.
So next time you’re staring at a stack of planks and wondering how much to buy, you’ll know exactly what to do. Happy woodworking!