If you tuned into Instagram this past weekend, you saw that I spent many hours seated at my sewing machine! I’ll show you what all I made on Thursday, but today I wanted to pop in with another installment of my Home Decor Sewing School series. This series is all about breaking down common techniques and projects that are used to make basic home decor items. I am not an expert sewer, but mastering these basic techniques has allowed me to create unique and perfectly-tailored items for our home, time and time again. We’ve covered how to make piping and pillows shams. Today I want to show you how to sew boxed corners, allowing you to transform a flat piece of fabric into a 3-dimensional one that can fit onto cushions, tables, and more!

Learn how to sew boxed corners: the simple sewing technique for giving a flat piece of fabric corners to fit over tables, cushions and more!

Why Would You Need To Sew Box Corners?

Some of you may be scratching your head thinking “Why is it so handy to know how to sew box corners?” Well…mastering this one, very simple technique opens up a whole possibility of projects for your home. Even if you’re not following a specific pattern or project tutorial, understanding how to give a flat piece of fabric dimension via corner seams allows you to make really tailored fabric items such as slipcovers, cushion covers, sheets, tailored table cloths, and more! Here is just a sample of projects I’ve done in our homes over the years that have all used the boxed corner technique.

Learn how to sew boxed corners: the simple sewing technique for giving a flat piece of fabric corners to fit over tables, cushions and more!

Barstool Slipcovers

Chair Slip Covers | Ottoman Slip Cover | Boxed Cushion Cover | Crib Sheets | Barstool Slipcover

Once you understand how to sew fabric together to make a simple corner seam, your eyes really will be opened to the various projects you can now do. I promise this one is a simple one…here is what you need to get started:

Tools needed to sew boxed corners: rotary cutter, rulers, fabric, pins, and thread

Materials Needed to Sew a Boxed Corner

  1. Fabric
  2. Coordinating thread
  3. Rotary cutting set including a self-healing mat, long ruler, and rotary cutter
  4. Square cutting ruler (optional)
  5. Pins and sewing machine (not pictured)

Measuring and Cutting Your Fabric for a Boxed Seam

I’ve shared with you all before that I’m not really one for following patterns. I like to make things up as I go; I tend to look at my item and figure out how to get the look I want. That’s why understanding this technique is so handy! But since I don’t have a specific project I’m sharing this technique for, I’m going to speak in some generic abstracts. Let’s say you want to make a tailored table cloth, an ottoman slipcover or even a stool cover, you will need to measure your specific item that you are covering as described below to figure out how much fabric you need AND exactly what dimensions to cut the fabric down to:

diagram showing the formula for measuring and cutting your fabric

A note here on letter C – the amount needed for hem and/or seam allowance. This measurement is somewhat up to you based on what you are doing and how much of a hem/seam allowance you like to work with. If you’re making a table cloth or slip cover, a 2-3″ hem is probably sufficient. If you’re going to be attaching another piece of fabric along the bottom (to make a full cushion cover, for example) then you may need only 1/2″ extra for seam allowance. Think about your project and how much excess fabric you will need here!

Once you figure out your dimensions for your specific project as described above, cut the fabric down using a rotary cutter and ruler

rotary cutter, ruler, and fabric on a self healing cutting mat

Next, you will need to determine how much fabric to cut away in order to make a perfectly-fitting corner seam. Use the graphic below to help you:

diagram showing the formula for measuring and cutting your fabricUpdate 6/2020: After some reader’s comments and experimentation myself, this equation has been slightly adjusted. I now recommend subtracting 0.5″ from your corner measurements to allow for seam allowances and ensure your cover fits your object perfectly. This seam allowance is for the surface of the cover (rather than the hem), so subtract it no matter the length of hem you use. The equation above has been edited to reflect this change!

In my sample project, the item I am covering is 6″ high (B). I then decided to give myself 2 inches for hem (C). As such, I used my square ruler to cut out 8″x8″ squares from all four corners of my fabric. If you don’t have a square cutting ruler, you can use a regular ruler and a pen to mark your dimensions.

rotary cutter, ruler, and fabric on a self healing cutting mat

Next, cut out the square according to the dimensions you determined above!

rotary cutter, ruler, and fabric on a self healing cutting mat

How to Sew Boxed Corners – Method 1 (The Really Easy Way)

With your square of fabric cut away, it’s time to sew up your corners! Simply bring one of the cut out edges to the other (on the same square).

red fabric with stars

For this method, you’ll want to make sure your RIGHT sides are together and the top and sides line up perfectly. You may certainly pin this seam in place if you need to.

folded piece of fabric and sewing pins

Using your sewing machine and coordinating thread, sew the two edges of the cut-out square together using a 1/2″ seam allowance.

fabric being sewn together in a sewing machine

If your fabric frays or you want to keep the edges from rolling, you can either use a wide zig-zag stitch or a serger to finish the raw edge. Repeat the process on all four corners of your project.

close up image of fabric seam

Once turned right-side-out and pressed, you’ll have lovely corner seams that allow your fabric to now fit perfectly over a table/cushion/whatever!

slip cover with a boxed corner seam

How to Sew Boxed Corners – Method 2 (French Seams)

The method I described above is super simple, friends. I mean it. You can have all four corner seams done in about 10 minutes. This next method (French seams – ooo la la!) is almost as easy and almost as fast; it just has a few extra steps to help make your seams a little more durable and polished!

You will cut out your fabric and corners exactly as described above. This time, however, instead of bringing the RIGHT sides of fabric together, you will bring the WRONG sides of your fabric together. It’s still the two edges of the cut-out square, just brought together the other way.

red fabric with white stars folded next to an iron


This time, sew the seam with a 1/4″ seam allowance…

piece of fabric in a sewing machine

Next, use a ruler and rotary cutter to trim away 1/8″of that seam allowance (essentially trimming it down by half).

rotary cutter, ruler, and fabric on a self healing cutting mat

Now, take that same seam and turn your fabric inside-out so that your RIGHT sides are finally together. You’ll notice below that this essentially flips your first seam to the inside. Press this seam with a hot iron to make sure it’s nice and flat.

piece of fabric turned inside out

Go back and sew the seam again, this time with RIGHT sides together but again using a 1/4″ seam allowance.

piece of fabric in a sewing machine

When done, you will notice that the raw edges are caught in between the two seams, meaning you don’t need to serge or zig-zag to clean up any raw edges.

close up up a seam on a piece of fabric

Again, once turned right-side out, you’ll end up with a lovely boxed corner seam!

char slip cover with a boxed corner seam

How To Select A Sewing Method

Which method to use is mostly a matter of preference and the type of fabric you’re using. This red star fabric is a flannel that frays like crazy. And since it’s going to be washed a ton, I chose to use Method 2 which enclosed the raw fabric edge into the seam. This way, with the loads and loads of washing it’s sure to get…I don’t need to worry about the fabric (and therefore the seam!) ultimately washing away! Sneak peek:

red crib sheet inside a crib

More Cushion Resources!

If you’re using the box corner method to make new cushion covers, here are some other tutorials that may help:

Once you master how to sew boxed corners, I swear your eyes will be opened to potential projects all over your home! With some precise measuring and cutting, you can make tailored covers for just about anything. Sure there are other ways to create covers like the ones I’ve shown here, but this most-basic technique will get you off and running in no time!

Back here on Thursday, I’ll show you more details on what I was making here as well as LOTS more fun fabric projects for baby. See you then!

See You Soon!