How to Sew Perfect Fit Box Cushion Covers

This past week I’ve been working on lots of different things for our ORC living room makeover, but I’ll be honest, I’m making pretty slow progress. One project I am working on is all new cushion covers for both of our vintage chairs so I thought for this week’s post I would share a tutorial on how to sew these yourself!

These are probably a more advanced home sewing project, but totally worth it if you want to save money on custom cushion covers (and are not afraid of a few zippers). 

I recommend using an online box cushion fabric calculator to figure out how much fabric you will need to buy for your project. You could probably figure this out on your own, but I am lazy so I don’t.

Materials & Tools

  • Fabric of your choice
  • Thread
  • Zipper
  • Cushion to cover
  • Sewing machine
  • Scissors
  • Fabric tape measure

Optional, but helpful:

  • Chalk marker
  • Cutting mat
  • Rotary cutter
  • Quilting Ruler

Box Cushion Cover Math

Before you get started with your new box cushion cover you will need to do some math to figure out what size pieces you will need to cut. Measure and make a note of the width (W), depth (D) and thickness (T) of your cushion. For this tutorial I am assuming that the zipper will run along your width measurement.

For each cushion you will need to cut four pieces of fabric. Here’s the math I use to figure out the right sizes:

Top & Bottom (2 pcs): Take your width (W) and depth (D) and add 1” to each measurement.

(W + 1) x (D + 1)

Zipper casing (1 pc): Add 8” to your width (W) and add 3” to your thickness (T) measurements.

(W + 8) x (T + 3)

Boxing (1 pc): Calculate the total circumference (C) of your cushion and subtract the cut length of your zipper casing determined above and add 1”. Add 1” to your thickness (T) measurement.

(C – (W + 8) + 1) x (T + 1)

For my cushion that had the measurements 20.5″w x 15.5″ D and 3″ T – I cut the following pieces:

Top & bottom (2 pcs): 21.5″ x 16.5″
Zipper casing (1 pc): 29.5″ x 6″
Boxing (1 pc): 44.5″ x 4″

Cutting your Fabric & Important Markings

If I can, I try to use my rotary cutter, ruler and cutting mat when cutting fabric. This gives me nice straight and accurate cuts. If you do not have these tools, I recommend marking your cut line with chalk and using very sharp fabric scissors.

Once you have cut your top and bottom pieces make a small notch in the centre of the back edge. This will help you keep track of the front and back of each piece where the zipper will be placed.

After cutting your zipper casing fold it in half widthwise bringing to the two ends together. Cut a small notch on both sides of the fabric along the fold line to make the centre point. Now cut this piece in half lengthwise to create the two sides of your zipper casing. The notches will help you remember which are the outside edges.

Sewing the Zipper Casing

Start by turning your inside edge (the one without the notch) in by 1”. If your fabric will hold it you can simply press this fold into place. My fabric was so stiff I used a pin to keep the fold in the right place.

Using a zipper foot on your sewing machine, attach your zipper to the folded down edge. Repeat with the other zipper side and peice of your zipper casing. 

Once you’re finished you should have a finished piece the same width as the piece of boxing you cut – oooh the magic of math (my dad would be so happy I just said that).

Complete the Cushion Boxing

Pin your zipper casing right sides together to your piece of boxing at both ends. Sew together using a ½” seam allowance to create a big loop.

Attach the Top and Bottom

Starting with the top, align the notches you cut and pin right sides together. Work your way around to just past the seam where your zipper casing and boxing meet and place another pin – this is where we are going to start sewing. I like to start here just in case I get around the entire cushion and need to adjust the length of the boxing at all. 

In order to get your corners looking great, add a small snip in the boxing right before you reach the corner. Bring your needle about ½” from the edge and, with the needle in the down position and the pressure foot raised, turn your fabric. The snip allows the boxing to turn nicely creating a sharp corner. Make sure the fabric is clear and continue sewing. I find that as I work my way around my back centre notches don’t always line up again BUT I hardly ever need to adjust my boxing.

The process for adding the bottom piece is essentially the same, however after I line up the back notches I like to make sure that both my front corners are lined up nicely as well. I will also start sewing just before the first corner as well, because that front edge is the most noticeable. 

Once you’re done sewing you will end up with an inside out cushion cover – simply unzip, turn right sides out and stuff with your cushion! 

I hope you found this tutorial helpful! I hope to have a video posted of the same tutorial soon on my YouTube channel.

Thanks for visiting and make sure to check out all the other makeovers taking place as part of this round’s One Room Challenge.

5 thoughts on “How to Sew Perfect Fit Box Cushion Covers”

  1. Hi, thanks for your tutorial and helpful
    math calculations.
    One comment and a question, both of which are related to the problem I often experience in trying to get the top and bottom pieces properly attached to the box Loop. The comment is that I usually don’t attach the ends of the box panel to the zipper panel until the very end after I’ve sewed both top and bottom panels to the boxing and zipper panels so I can adjust the fit. In the past when I’ve created one whole loop and then trying to attach the top and bottom I somehow end up with a slanted cover in which the top and bottom panels don’t align.
    Hope this makes sense.

    My question for you is regarding the way in which the box panel and zipper panel should be cut with regards to the fabric salvage. My guess is it should be cut lengthwise across the width of the fabric to minimize stretch. Could you address this question?

    Thank you!

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