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1. Start with your project idea
It can be a full plan or just a simple sketch

2. Make a parts list
Then determine the board footage of each part

3. Add it up
Then estimate a waste factor for some margin to work with

Don’t Like Math? Here’s An Easier Way

Get our “Project Planner” worksheet to do the math for you.
Free Download (.xlsx file)

In an ideal world, you wouldn’t buy lumber for a project – instead you’d sort and pick from a stockpile of wood you’ve accumulated in your shop or shed, and then maybe buy a little bit to fill in here and there. But not everyone is fortunate enough to have the space (or the pleasantly supportive better half) required to store a couple hundred board feet of lumber.

If you must buy material according to the needs of each project, know this: figuring out how much board footage to get is an exercise in estimation. You have to do a little math and a little guessing, and the result is just an approximation. “This project is going to require about 11 board feet.”

1. Start with a Project Idea, Plan or Sketch

Your plan can be as simple as a napkin sketch or as sophisticated as a SketchUp or magazine plan, or anything in between. It should essentially answer the question: what’s the overall size of this project?

You just need to have a concept of the general size. Then you can step your way into the details. Once you know, for example, that you want to make an end table about 20″ square (or whatever) you’ll be able to determine the size of its parts, and therefore how much wood it’s going to require . . . and ultimately how deep into your budget you’ll need to dive.

If you start with a sketch or “napkin plan”, it will probably start out crude, awkward, or kind of embarrassing. That’s okay, it’s just a draft. You’ll revise and refine things as you get your hands wrapped around the project. A plan from a magazine or book will have a lot of the heavy lifting done for you.

2. Make a Parts List

Now you’ll have to start putting some thought into things. Use a spreadsheet (download this free template if you want), or an old fashioned piece of paper and pencil, start jotting down the individual parts to your project. Let’s use a basic end table as an example: top, legs, and aprons. Put down the sizes of each of those parts, like this would work:

Part
Rough
Thickness
Final
Thickness
Width
Length
Quantity
Net
Board Footage
Top 4/4 3/4″ 20″ 20″ 1  2.78
Legs 6/4 1-1/4″ 1-1/4″ 18″ 4  .78
Aprons 4/4 3/4″ 2-1/2″ 17-1/2″ 4  1.25

TIP: To calculate board feet: rough standard thickness X actual width X actual length divided by 144.  Use the thickness of the material you intend to start with, not end with. For example, the 3/4″ top will start from 4/4 lumber. The legs will start from 6/4 lumber. This is because you must start with 4/4 lumber in order to achieve a final 3/4″ thickness; likewise, you must start with 6/4 lumber to achieve a final 1-1/4″ thickness. See this page for more about board feet.

3. Add It Up, then Apply a Waste Factor

Now you’ll determine how much 4/4 to buy, how much 6/4 to buy (etc.) So first add up the board footage of the parts that come from the same thickness of lumber. In the example here, you should come up with:

4.03 board feet of 4/4

.78 board feet of 6/4

That’s the exact amount that the parts equate to.

Now add some extra – consider multiplying by at least 1.5 or 2. After all, to end up with those parts, you have to start with boards that are larger. Round off to the nearest whole number, too. You’ve arrived at about the board footage you’re going to buy, or a target amount, so there’s no sense in talking in terms of decimals or fractions at this point. It’s not the precise amount, as that is determined once your boards are selected and measured. Since boards in the lumber pile vary in width and length, you may be aiming to pick up 8 board feet and what you end up selecting could be something more like 7.89 or 8.62 or 10.18. It just depends on what the lumber pile provides and which pieces appeal to you. But at least you have a really good idea of what your project needs.

Lumber
Thickness
Net
Board Footage
Approximate
Footage to Buy
4/4  4.03 8
6/4  .78 3

Now that you’ve approximated your the footage you need you can get a pretty good idea of what the project will cost you. And if you’ve made an adequate estimation, you’ll have plenty of material to work with to create a project you’ll be proud of. You know what’s worse than buying too much wood for a project? Not having enough to complete it.

If a factor of 2 seems like a lot, there’s more to think about than just the parts of your project. To build a really great project, you need enough material to:

  1. Mix/match grain patterns or color
  2. Cut around parts of boards you don’t like
  3. Test your stains or finishing process
  4. And, believe it or not, you’ll probably make a mistake once or twice and need to cut an extra part.

In a real life example, let’s say you want to cut a board down to 4″ x 48″ from a piece that was 6″ x 48″. That’s not terribly uncommon, nor is it unreasonable. Yet, that’s 33% waste – or in other words a 1.5 waste factor without a defect to work around.

After you build a few projects, you’ll discover how realistic it is to not just plan for enough wood, but more than enough.

  • Ahmed

    How do you use this formula for cubic metre?

  • Kelly Linton-Selkirk

    The movers lost the top to a mid century executive desk .What would it cost to buy a solid wood board 48*36*2? I think the desk is made with oak.

  • cmbindc

    How do you convert board feet to square feet?

    • Art Lurvey

      You don’t. Board feet is a measure of volume. Square feet is a measure of area.

    • Depends on the thickness, but it can be done. Divide the board footage by the lumber’s rough thickness and that will give you the square footage.
      Three examples:
      20 board feet of 4/4 lumber: 20÷1 = 20 square feet.
      20 board feet of 8/4 lumber: 20÷2 = 10 square feet
      20 board feet of 6/4 lumber: 20÷1.5 = 13.33 square feet

      Board footage is the same thing as square feet times thickness.
      Board footage is also a measurement of volume for lumber that’s 1″ or thicker. So if you’re dealing with thin lumber like 1/2″, 5/8″ or 1/4″, you would be using square feet as your measurement any way. No conversion necessary.

  • J

    Fairly certain the sample “Legs” calculation was done using 5/4 rather than 6/4 rough thickness in order to get the 0.78 bd. ft. Otherwise, very helpful.

    • Ah yes! Nice catch. The calculation is done simply based on the exact finished sizes, which is, yes, 1.25. But there’s a reason why I put down 6/4 as the raw material to use.

      While 1.25 is the number represented by 5/4, to actually make legs that are a full 1.25″ you can’t use 5/4 lumber. It doesn’t yield a full 1.25″ after milling. Must start with 6/4 or something larger. That’s why I’ve indicated that 6/4 is the raw material to start with. Make sense?

      Likewise, 4/4 lumber doesn’t yield a full 1″ after milling.