DIY Fitted Window Seat Cushion

Dalmatian dog lying on DIY fitted window seat cushion
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How to make a DIY fitted window seat cushion. A comfy window seat is a perfect perch for people or pampered pets, like Humphrey. Now that the crafts stash has (finally) been semi-unpacked at the new house and the sewing machine liberated from moving box prison, the long awaited home décor DIYs, makeovers, and upcycles have begun. Our master bedroom has a window seat, plainly finished in the same paint as the walls. Blah! Not comfy at all! Time to make Humphrey his long overdue custom fitted DIY window seat cushion for basking in comfort.

Supplies and Materials

This DIY window seat cushion is basically a giant version of one of our fitted boxed corner dog beds, sized to perfectly fit the built-in seating area in the window nook.  It was made using foam (cut from a basic mattress, just like my dog bed insert hack), suitable fabric, coordinating thread, basic sewing supplies (including cutting tools and a sewing machine), and Velcro / hook and loop for the closure.

To make a similar DIY fitted window seat cushion, you will need:

  • Foam (plus cutting supplies, if/as needed – see below)
  • Fabric
  • Straight edge (either as a cutting guide or to mark a guide line)
  • Measuring tape
  • Complimentary coloured thread
  • Velcro / hook and loop tape (closure)
  • Sewing machine and general cutting / sewing supplies
  • Iron and ironing board (optional, but recommended if fabrics allow)

Fabric Selection

As with all things pet-friendly, removable and washable covers make life easier and cleaner.  Fabric selection for this seat was easy for once (and “free”). I had a large piece of the same velvety grey upholstery fabric used in our custom pet basket bed cushion inserts and easy envelope pillows (the velvet makes these irresistibly comfy) big enough to cover a window seat cushion.

Foam Selection

I needed a large piece of foam for the cushion body itself. The seat isn’t going to be a high-use area (although sunbeam-loving window-watcher Humphrey may have other ideas) so it didn’t need a particularly high-performance foam or resilient insert. It’s an easy way to make a foam cushion insert. As a lesson learned when shopping for the pets’ beds, I waited for a great sale on a good quality foam mattress instead of buying custom cut-to-measure foam. In the absence of special tools, foam cuts very well with just a simple bread knife or an electric kitchen knife, if you have one.

Measuring and Cutting Foam for a Window Seat

  • Measure the bench seat area carefully.
  • Lay foam flat. Measure and mark the cutting dimension(s).
  • Double check everything before you cut!
  • Cut foam. We used a kitchen bread knife.
  • Dry fit the foam in position on the seat to ensure it fits correctly in position.
Cutting foam for a custom fitted DIY window seat cushion

Putting Our Foam Offcuts to Good Use

If you’re a regular reader, you’ll know how much I hate wasting materials. I used the little offcuts to make some crazy square-ish bolster pillows for Humphrey. He likes resting his head on something to look out from a floor bed through the full-length office window while I work.  They make a perfect chin rest. They’re pretty handy as people pillows too, when cuddling on the dog beds!

DIY bolster head rest for dog bed using a foam offcut

Sewing a DIY Fitted Window Seat Cushion Cover

Keeping Things Simple

I wanted the finished cushion to be as clean and simple as possible, with minimal visible seams and no piping or tufting. They just gather fur at our place! Rather than creating a true box cushion cover using top, bottom, and side panels, I opted to simplify things by boxing the corners on a wrap-around cover. Only the front of the cushion is visible when in place on the bench, other than one little bit at the left corner (exposed overhang, shown below), so the visible side seams weren’t an issue. This method is much quicker and easier to cut and sew, especially since I was working with slippery velvet that liked to move and refused to hold when ironed. Grr.

Our Window Seat Cushion Cover Design and Construction

Our cushion cover was made from a large single piece of fabric. It has an overlapping rear closure through which the cushion can be inserted and removed if the cover needs to be cleaned. I opted for Velcro-style hook-and-loop in lieu of fitting a zipper, using some of my large craft stash rolls. Hubby bought them from AliExpress (affiliate link) when I had difficulty finding affordable hook and loop in our local shops. 

The construction is like our dog bed covers, combining single piece construction with a rear overlap closure. Getting a snug giant cushion cover required a little extra care on fit-checks and boxing, but not too difficult with a little patience. Even though I’ve made a lot of different cases and covers over the years (getting better every time!), I still like to do a check fit at each stage as I work. Just in case! Mistakes and rework suck, but better when minimised if ever needed.

Sewing a case for a DIY custom fitted window seat cushion

Measuring and Cutting

  • Measure and calculate the fabric requirements to fully enclose the cushion on all sides.
  • Add additional allowances for the seams, finishing the edges on the rear panels, and overlap of the rear closure.
  • Double check all measurements and calculations prior to cutting.
  • Cut fabric to required dimensions.

I included an extra wide doubled-over seam for the outside of the rear flap. I know. No one will ever see it or know it’s there, but it echoes the styling used on the same DIY velvet throw cushions and pet basket bed cushions. It also allowed me to first attach the outside hook and loop to what then became the underside of the fold, concealing the back side of the stitching. Sewing hook and loop can be tricky at the best of times, but even more so with slippery velvet.

Preparing the Rear Closure Flaps

  • Finish rear closure edges using your preferred style of hem.
  • Double check your measurements and confirm placement for hook and loop.
  • Position and sew hook and loop into place (see alternative assembly notes below), ensuring that the cushion cover will fit tightly when enclosed and fastened.

You can run the hook and loop so that it encroaches on the area to be sewn and boxed (no need to waste more by going all the way to the edge). Alternatively, you can stop shorter for less use (and potentially easier sewing and boxing). There will still be plenty of hold with a small gap at each end. The difference can also be sewn, if you wish.

Sewing the Case

  • Close the rear as it would be in a finished cover. Flip the loop of fabric so it faces wrong side out.
  • Double check your measurements, then carefully position the cover right side in in prepration for sewing the sides. Laid flat, the closed loop of fabric should be folded PRECISELY where you want the middle of the front and back sides to be when complete.  The fold lines will be the middle of the front and back (closure panel) in the finished cover once sewn and boxed. Pin to secure.
  • Sew the sides together along the seam allowances. Trim excess, if/as needed.

Boxing the Corners

  • Starting with one corner:
    • Position by pulling the fabric sideways from the seam so that the seam line is centred evenly from the point, forming a triangle. Ensure that it is flat and even.
    • If the fabric allows, iron to ensure that the seam is pressed flat and the square holds position.
    • Measure across and mark a straight line at the point where it is the depth you want for the boxed corner (in this case, the cushion thickness).
    • Sew across the marked line.
    • Trim loose threads and excess.
  • Repeat for the other corners, taking care to ensure that the shared seams are flattened to fall in the same direction for a smoother line in the finished cover.

Extra care is required when boxing the corners with your overlapping rear panels and hook and loop. Ensure everything is fitted smoothly in the as-closed position before sewing. Double check that nothing has been accidentally shifted or bunched before trimming.

Filling and Using the Cushion

  • Open the hook and loop closure and reverse the cover right-side-out.
  • Squeeze the foam and wrangle it into the cover through the opening, taking extra care to ensure the corners are tightly in position.
  • Close up the cushion. 
  • Place it into position on your seat, and enjoy!
DIY custom fitted window seat cushion with removable cover

Alternative Assembly Options: If you aren’t confident with the precision needed on measurements/fit for finishing the rear first, you can half sew the sides from the front fold-over, box the front corners, and do a fit-check to confirm your measurements before doing final cuts, edges, and Velcro on the rear closure. make sure you line your stitch path up when you finish closing out the sides. I’ve tried all both methods over the years. Done carefully, the results look more or less the same either way, so go with what feels right for you! You can also make the complete envelope and then sew the hook and loop after, if the cushion is large enough. to freely access the flaps.

DIY custom fitted window seat cushion and removable cover

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