What is board foot in lumber?

A while back, the following question was posted to our forums, and it brought to light that we don’t have much covering the topic of board foot calculations. It’s a fundamental skill that often is taken for granted by experienced woodworkers, but confounds beginners.

How would I calculate the amount of board feet I need to purchase? Say I am making a face for a floating shelf, 3/4 in. by 2 1/2 in. by 6 in. Do I just punch those numbers in and get the answer? Or do I figure out what raw stock size I need and work from there?

Except for dealing with dull tools, lumberyard lingo is one of the most frustrating things when getting started in woodworking. Honestly, when you’re looking through a stack of lumber the important thing is to find the best board for the project. Start thinking about board feet only after you have inspected the size of the board and its grain, looked for any imperfections, and made sure that you’re going to be able to get the parts you need out of that board.

You really only need to worry about board foot calculations when you’re paying for lumber at the lumberyard. Since most lumberyards sell boards at random widths, they can’t sell using a per-board price, or a linear price like big box stores. The same way you pay for deli meat by the pound, you pay for lumber by the board foot. It’s the lumberyard’s way of calculating the actual amount of wood you’re buying.

Here is a quote from Steve Scott’s article “The Language of the Lumberyard” that explains it well.

“Lumberyard operators say one of the biggest challenges new customers face is in understanding the board foot—the basic unit of measurement for roughsawn stock. The board foot (144 cubic in.) is confusing because it measures a board’s volume, not its length. This means that a piece of stock 1 ft. long can contain more than 1 board foot of material.

A good visual way to understand 1 board foot is to picture a board 1 in. thick by 12 in. wide and 12 in long. Add an inch to the board’s thickness, and you now have 2 board feet. To calculate a plank’s board footage, multiply its thickness by its length and width (all in inches) and divide the result by 144. In contrast, surfaced lumber is typically sold by the linear foot, a simple measurement of a board’s length. The price per foot will vary according to the board’s width and thickness.”

The only time that I worry about calculating board feet is when I’m trying to see if I can afford to purchase material for a project–or in the ballpark at least. I might look at a design, roughly add up how many board feet of lumber that project will take, and then add 50% to 100%. Why the added percentage? If you’re being picky about parts, it’s amazing how fast stock gets used up.  Add in mistakes, redesigns, hidden defects, and the fact that I’d rather have lumber left over than wind up needing one last piece, and 50% more than you calculate is a responsible place to start. Your mileage may vary.

Then I’ll call the lumberyard, get the board foot price for the species I’m looking for, and calculate about what it will cost for my project. Even after all of the calculations, I have come to expect that my lumber purchases will wind up costing more than I expect.

Lumber-buying strategy will give your project a smarter start

The Wood Whisperer goes back to the basics with a simple explanation of how lumber is cut and sold

When building a project from wood, it makes sense that you would need to know some special jargon. After all, as you estimate the amount of materials you’ll need, you’re essentially describing an abstract three-dimensional project that still only exists in your mind. How you express what you need is an important factor in making sure you estimate the overall cost correctly and end up with the right amount of materials.

One of the most commonly misused phrases we’ve heard at our lumber stores is the term “board feet.” In this article, we’ll break down exactly what that means (it might not be what you think it is!), how to calculate it, and when is the right time to use it.

But first, let’s start with some definitions of things that aren’t board feet – but are sometimes mistaken for such.

Simply put, the term “linear feet” is a measurement of length. That can be the length of the amount of fencing you want to install, or the length of an individual board. You’ll use this term when estimating the amount and cost of materials you’ll need for a project.

Be clear about what “linear feet” is referring to as you scope out your project. Calculating the cost of a “fence that is 100 linear feet long” is very different than discussing a “board that costs 10 cents per linear foot.” If you’re determining cost and materials on your own, ask the team at the lumber store to double check your work. They’ll make sure you’re not drastically off-base.

One additional note: you may hear people saying, “lineal feet” instead of “linear feet.” Though they mean the same thing, the correct term is linear feet.

Sometimes we hear customers mistakenly use the term “board feet” when what they are actually referring to is area. When calculating the amount of materials you need for large surfaces (ex. exterior siding), knowing the area of the space you’ll need to cover is the first step. This is where middle school math comes in handy.

Surface area calculations are simple: Length x Width, which gives you total square feet. Don’t worry about subtracting anything out for windows and doors (better to have a little too much wood than not enough) and always buy an additional small percentage to account for downfall (the occasional warped or discolored board that you don’t want to use).

The true definition of “board feet” is not a calculation of length. Believe it or not, it’s a calculation of volume. The term is most often used by lumber producers who need to determine how many board feet they can obtain from each tree they harvest. Therefore, this is not a term that you will likely ever need to use at the lumber yard.

However, if the term has piqued your curiosity, here’s a quick run-down.

One board foot is measured as 1x12x1 . Notice that this board is a square (1 foot equals 12”).

A 1x6x1 has 0.5 board feet. This board has half (0.5) the volume of the 1x12x1 board.

Sometimes it helps to visualize the “missing” half of the board foot.

A 1x10x1 has 0.833333 board feet (We multiply the 1” thickness by the 10” width then divide by 12 to calculate our board foot factor (BFF), which is the number of board feet per linear foot. So, this 1’ long board has 0.833333 board feet of material.

A 2x6x1 has …one board foot of volume. That’s right, ONE board foot.

Why? Imagine that you started with a 1x12x1, which we know equals one board foot. Then imagine you moved 0.5 board feet from the right side of the board and stacked it on top of the left side of the board to create a 2×6. The volume of material didn’t change.

A 2x8x1 has 1.333333 board feet. Since a 2×6 has one board foot, divide this 8” width by 6 to calculate the board foot factor of 1.333333. A 2x4x1 has 0.6666667 board feet Since a 2×6 has one board foot, divide the 4” width by 6 to calculate the board foot factor of 0.6666667, etc.

To calculate the BFF: (Thickness x Width) /12.  Or, use this handy Board Foot Factor (BFF) table.

Now let’s look at how Board Feet works for more traditional lengths of lumber.

To calculate total board feet: Board Foot Factor x Length

A 1x12x10 board has 10 total board feet in it: the board foot factor (BFF) of a 1X12 is 1. Multiply 1 by the length of 10, which gives total board feet of 10.

A 1x6x10 board has 5 total board feet in it: the board foot factor (BFF) of a 1×6 is 0.5. Multiply 0.5 by the length of 10 which gives total board feet of 5.

Tip: Both of these previous boards measure 10 Linear Feet (LF) because, remember, LF does not take thickness and width into consideration.

A 2x4x10 board has 6.66667 total board feet in it: the board foot factor (BFF) of a 2×4 is 0.666667. Multiply 0.66667 by the length of 10 which gives total board feet of 6.66667.

A 2x4x14 board has 9.33333 total board feet in it: The board foot factor (BFF) of a 2×4 is 0.66667. Multiply 0.66667 by the length of 14 which gives total board feet of 9.33333, and so on…

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Using the correct terms as you talk about your project helps our lumber specialists make sure you’re buying what you need. So, unless you’re thinking of getting into the logging industry, the measurement terms you’ll need are probably linear feet and square feet, but unlikely board feet. That said, talk to the team at the lumber yard about your projects so they can make sure you’re covered.

Sawmillers and most suppliers use board feet as a unit of wood measurement. It's important for you to know and understand how to calculate board feet and board feet pricing for your sawmill business.

The basic calculation for board feet is:

Thickness x Width x Length / 12 = Board Feet 1" T x 12" W x 1' L / 12 = 1 Board Foot

A 2 x 4 - 10' has 6.667 board feet:

2 x 4 x 10 / 12 = 6.667 Board Feet

A 2 x 10 -16' has 26.67 board feet:

2 x 10 x 16 / 12 = 26.667 Board Feet

To calculate the board footage for a number of pieces at one time:

PCS x T x W x L / 12 = Board Feet

To calculate the board footage in an 84 piece unit of 2 x * - 12:

84 x 2 x 8 x 12 / 12 = 1,344 Board Feet

It's important to remember that 5/4 stack-like deck plank, is considered thicker than 1" stock. This means when calculating board footage for 5/4" stock you must use 1.25 as the thickness instead of 1.

For example, to calculate the board footage of a 5/4 x 6-14' piece of material:

1.25 x 6 x 14 / 12 = 8.75 Board Foot

Compare this to the board foot calculation for a standard 14' board:

1 x 6 x 14 / 12 = 7 Board Foot

Another way to quickly calculate board feet is to memorize the board feet in each lineal foot of standard dimensional material. For example, there is .667 board feet in 1 lineal foot of 2 x 4. To calculate the board footage by the length:

.667 x 10 = 6.67 Board Foot

The table below lists the board feet in a 1' piece of lumber for each dimension:

When calculating the board feet in a random width product, such as oak boards, you use the actual width in inches, not the nominal width. Since you use the actual width in inches in the calculation you also enter the length in inches as well, then divide by 144, instead of 12  because there are 144 square inches in a square per board foot.

Let's say you have a piece of random width oak with an actual size of 7/8" thick by 7 3/4" wide by 63" long. The board foot calculation for this piece would be:

1 X 7.75 x 63 / 144 = 3.39 Board Feet