My previous office chair was covered in snags from my cat jumping and scratching on it, not to mention cat hair. I originally made this for utilitarian purposes to keep my new chair nice, but ended up liking the fun pattern in my office setup.

Because the seat is connected to the chair and is attached at the underside, you need a cover that slides on from the top. These instructions should work for most office chairs that have upholstered seats (like a fabric covered cushion) that are separate from the chair's back.

A warning: I made this with a bit of eyeballing and trial and error. If you don't feel confident constructing this, I recommend using some extra fabric to make a practice cover and figure out the exact measurements before sewing with your nicer fabric.

Materials

You will need about a yard of fabric. I got away with 3/4 yard, but it will depend on your chair.

You will also need some narrow 1/4 inch or 3/8 inch elastic.

Measure and cut

Cut a square (or rectangle) large enough to go over your seat and wrap a few inches underneath. I measured it side to side and front and back at about 25 inches, so I cut a 25 inch square.

Fold your fabric in half and cut rounded corners on each corner. The exact radius will depend on your chair, but remember you want the fabric to be bigger than the seat. (I warned you there'd be eyeballing…)

Because my chair is narrower in the back, I trimmed off a narrow wedge, creating a trapezoid. This is optional because once you add the elastic, it will stretch to fit. Small differences won't really matter.

At this point, you can lay the fabric over your chair and see if it looks generally the right size and shape. I ended up trimming a bit off the corners since it looked like it was hanging down too much there.

Sewing

If you want, you can serge or finish the edges to prevent fraying. But I won't judge you if you don't – no one is going to see it anyway!

Starting from the apex of a corner, pin 2 pleats toward the left and 2 pleats toward the right. Each pleat should be about 5/8 inch.

Repeat for each corner and sew in place.

Here's how it should look once you've sewn pleats onto all 4 corners:

Test the cover on your chair again. It should easily fit over the seat, but hang down loosely on the sides in between the corners.

Next measure the length of each side between the pleats. Cut a piece of elastic about 2/3 the length of the side. It should easily stretch to the full width.

(My 4 sides varied by about an inch, but this is fine. I cut the elastic the same length for all of them.)

Pin the elastic to the straight, unpleated sides. Add another pin or two in the center to make sure the elastic's stretch is evenly distributed.

Sew the elastic to the fabric with a zigzag stitch. While you are sewing, stretch the elastic to match the fabric. When you release it, it will scrunch up.

That's it! Put it on your chair and check the fit again. If it is too loose anywhere, you can add an additional pleat.