The Best Picture Frame Molding Calculator (Box Trim Made Easy!)

Picture Frame Molding Calculator

Let’s not waste another second. We know why you’re all here 🙂 Here’s the best picture frame molding calculator!

Be sure to read the tool tips on each field if you need further clarification.

This calculator is meant for calculating your box trim or wainscoting height and width for a single wall, since, as I mentioned in the step-by-step DIY picture frame molding post, each wall will most likely have a different box width.

And yes, this box trim calculator works for determining the width and height of a single box, if you have a space beside a window or doorway, like I did!

Seriously, this calculator is such a lifesaver and does all of the mental math for you! I really wish I had this the first time I was installing box trim…but now I have it for all future projects, and so do you!

Check out DIY Picture Frame Molding for the questions you need to ask yourself in order to come up with your box trim rules – which will greatly help in getting you started with using the calculator!

Box Trim Width and Height Formula

If you like to double-check your calculations, or simply do the math on your own, I’ve got you covered!

Here is the formula for figuring out how to measure for picture frame molding and determine the width and height of your boxes for your picture frame molding:

Box Width Calculation (use inches):

1. Begin with your total wall width.
   1. In my example, that’s 144″.
      
2. Subtract the total space between each box.
   1. If you have 3 boxes, there will be 2 spaces between them.
   2. So if each space is 6″, that’s 6 × 2 = 12″ to subtract.
      
3. Subtract the space between the wall and box (on the left and right).
   1. If you went with 3″ spacing here, that’s 3 × 2 = 6″ to subtract.
      
4. Now divide the remaining width by the desired number of boxes.
   1. You have 3 boxes, so divide by 3.

Adjust the numbers based on YOUR box trim rules and wall width!

For us, this looked like 144” – 12” – 6” / 3 boxes = 42” width per box.

Box Height Calculation (use inches):

1. Begin with the space between your chair rail and baseboard.
   1. In my example, mine was 37.5”.

2. Subtract the total desired space between the top and bottom of your box.
   1. If you went with 3” spacing here, that’s 3 x 2 = 6” to subtract.

For us, this looked like 37.5” – 6” = 31.5” height for each box.

My Exact Picture Frame Measurements

If you are curious about my exact measurements for my walls, here is an example! This is the exact picture frame molding spacing I used for my main wall.

And this is the final product! So good, right?!

DIY Picture Frame Molding Guide

Don’t stop at the calculations. I had an entire post on how to install DIY picture frame molding, taking you through step by step on taking your wall from bland to beautiful!

It’s jam-packed with helpful tips and all the products you need to easily install your very own picture frame molding, box trim, or wainscoting!