Okay - true confession time. In school, I was a theater rat... always in plays and musicals, always taking artsy-fartsy classes, including "How To Mime" or, as I remember it, "How To Pretend You're Stuck In A Box And Look Foolish Doing It." It's true, unless you're Marcel Marceau, you look really silly doing mime. So... no mime today. But, we are still making a box. In particular, a boxed corner. This is a sewing technique everyone should have in her/his arsenal. The boxed corner creates space in something that would otherwise be flat. For example, in a tote bag, you have a lot more room to put all your stuff if you create boxed corners. Basically, any sewn corner can be turned into a boxed corner with a few simple steps. 

If you sew two squares together, then turn them right side out, the square is still flat. If you were to stuff it with some filler, it would make a nice knife-edge pillow. If you want to turn your flat square into something with more dimension, you can add boxed corners.

We love the box corner here at S4H. Below are just a few projects made more appealing and functional thanks to their boxed corners. 

Kitchen Chair Cushions 

Vinyl Color Block Tote 

Structured Fabric Baskets 

Grocery Bag 

Toiletry Travel Bag

The basic box corner

We always use a light colored fabric with a bright colored thread so you can clearly see the steps of our technique tutorials. You would use the fabric of your choice with coordinating thread. 

In this example, we're assuming we’re working on a project that has sewn corners and is shaped like a square or rectangle. If you’re following a pattern or tutorial, the boxed corners (as well as the exact measurements) will be indicated.

1. Place the fabric right side together.
2. Using a straight stitch, and the indicated seam allowance, sew the side and bottom seams, pivoting at each corner. We used a ½" seam allowance.    
   
3. With the sewn fabric still right sides together, match the side seam with the bottom (or adjacent) seam to create a point or "peak." Place a pin in the seams to hold them together. It is very important that you exactly match the seams; that is what will make the lines of your finished corner look good. 
   
4. Mark the depth of the boxed corner with a fabric marking pen or pencil and a straight ruler, positioning your ruler so the depth is measured from side to side at the base of the "peak." Our boxed corner depth is 3” (more on how to determine measurements below).
   
5. Sew across the peak on the drawn line. Be sure to backstitch at the beginning and end of the seam.
   NOTE: Depending on the project you’re sewing, you may want sew across the peak two or three times to reinforce for added strength at corner. This would be an especially good practice for a bag.
   
6. Trim away the peak to ¼" - ½" from the line of stitching.
   
7. Gently pull apart the corner at the seamline to see the boxed corner take shape.
   
8. Turn the fabric right side out to really see what your finished boxed corner looks like!
   

Cut-out box corner

As with many sewing techniques, there’s an alternate way to create a boxed corner. Some people prefer to cut a square from each corner, then bring the seams together to sew the corner. You get the exact same finish as above, just in a different way. You may find this to be a better approach to sewing a boxed corner with heavier-weight fabrics. 

1. Place the fabric right sides together on a flat surface.
2. Measure, mark and then cut equal size squares from each corner. In our example, we cut 2" x 2" squares.
   
3. Using a straight stitch, and the indicated seam allowance, sew the side and bottom (or adjacent) seams separately (because you just cut away the corner you would have pivoted at!). 
   
4. In the same manner as the basic box corner above, carefully match the side seam with the bottom or adjacent seam.  Pin in place.
   
5. Sew along raw edge of the corner, using a straight stitch and the indicated seam allowance. Be sure to backstitch at the beginning and end of the seam.
   
   NOTE: Interestingly enough, you will sometimes see pockets shaped like this (with the two bottom corners cut out) except they use just one layer of fabric. Think about a cell phone pocket inside a bag; you need depth in the pocket for the phone... solution: boxed bottom corners.

Measurements

If you’re not following a pattern or tutorial that tells you the proper measurements, you will need to do some calculating to determine the size (or depth) of your boxed corner. It’s recommended you start with a shorter distance and go from there; you can always increase the size of box corner (especially if you’ve already trimmed away the fabric), but ya can't go smaller after you've made your cuts. As always, we recommend testing any new technique on scraps prior to starting on your project.

Basic box corner

With a basic box corner, the distance from one folded edge to the other at the base of the peak is the depth of the box corner. Remember, in our example above, we sewed 3” across the peak from fold to fold, which yielded a 3" box corner.

The farther away from the peak that you draw your line and sew, the deeper the box corner will be. Using a ruler to mark the stitch line will help you determine the depth, plus it helps you stay consistent on the other corner(s). 

Cutout box corner

When you plan to use the cutout box corner method, you need to pre-determine the size of the box corner. The most important thing to remember is: the size of the square you cut away is half the size of your finished box corner. In our example above, we cut out a 2" x 2" square, which resulted in a 4" box corner. 

The other detail to remember is seam allowance. You want to use the exact same seam allowance across the box corner seam as was used for your side and bottom (or adjacent) seam allowance.

As always, accuracy in cutting is key so the box corners are consistent in size.

A few additional helpful notes to remember about box corners

1. The deeper or larger the box seam, the shorter or more narrow the project.
2. The smaller or shorter the box seam, the less depth you will have overall.
3. If you’re making a tote bag, make sure to create identical box corners on your lining.

Contributors

Sample Creation and Instructional Outline: Jodi Kelly