Let’s Talk Wall Framing Math

You could say I’m Trumping today – since I’m building a wall    LOL!

There is a surprising amount of math involved in framing (building) a new wall. This math is very important because if your math for framing a wall is bad, your wall will be bad. Another fun detail that you should know when doing your math is that a 2×4 isn’t 2 inches by 4 inches, it’s actually 1.5 inches by 3 inches because of the drying and planing process. Now that we have that out of the way let’s examine the following problem:


I’m building a wall between a space that will eventually become 2 separate closets. The width is 69 and 3/8 inches. The height of the space is 92 and 1/2 inches. How many 2×4’s do I need and of what length?

At first this might seem fairly easy but lets consider the following; I will need 2 header pieces that are the full width of the space, and I will need 2 vertical side pieces, and a vertical piece every 16 inches on center. In the picture below you can see how our wall will look and I will then explain how we got there.



So – we know that we will have a top piece and a bottom piece and each will be at minimum 69 3/8″ so how many feet is this? We need to divide this by 12 since there are 12 inches per foot.

69 3/8 = 555/8, 555/8 divided by 12 = 69.375 / 12 = 5.78125 feet

Basically, I like to use calculators so I have to convert the fraction into something easy to punch into the calculator. 69 * 8 + 3 makes 555/8 which is the improper fraction equivalent of our original. Now, 555/8 in your calculator equals 69.375 which can then be divided by 12. This means I need 2 2×4’s that are 6ft long. These will be the top and bottom pieces.


How about the vertical pieces? How do I know how many I will need? Well, we know that we will have 2 side pieces and we will need to put pieces every 16 inches from one side to the other. Well, what is 69.375 / 16?

69.375 / 16 = 4.3359375, or about 4 boards

This means that in between our side pieces we can fit another 4 boards each 16 inches apart. In total, we will then require 6 vertical pieces but what height? Since the total height of the space is 92.5 inches, when cutting our vertical pieces we need to account for the depth of the top and bottom 2×4 pieces. Since each takes up 1.5 inches in depth, we will need to subtract 3 inches from the total height to get the height of each vertical piece.

92.5 – 3 = 89.5 inches tall

Now lets also convert this to feet to make our lives easier.

89.5 / 12 = 7.4583333

This means that we will need to get 6, 8 foot 2×4’s when framing our out wall. Just remember that when cutting the vertical pieces you must remove another 1/2 inch so that you have some play which makes installation easier.



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