The pillow case I am making is for a 20x20 pillow form from IKEA (Ullkaktus, $3.99).
Cut out desired size of fabric (2 pieces front and back) to fit the size of your pillow. For the 20x20 pillow, I cut my fabric 21x21 to allot for a 1/2 inch seam allowance.
Place zipper teeth side down on right side of fabric and pin.
Place remaining piece of fabric right side up with pinned zipper fabric face down on top of it.
Flip zipper up to match unpinned edge to right side up fabric.
Begin pinning zipper to other side of fabric. *I do not have a zipper foot, so I utilize a lot of pins to hold my zipper in place.
Once pinned flip open and make sure both sides are securely pinned.
Also test your zipper to make sure that it is working properly before sewing it to each side of the fabric.
Place your pinned zipper under your sewing machine and began to sew it to each side. Remove pins as you sew along. *Remember to back stitch at the beginning and end.
Repeat step 9 on other side.
Once complete, open fabric completely and test the zipper.
Sew the remaining three sides together using a 1/2 inch seam allowance. *You can sew over the zipper, just make sure that it's out of the way of your seam allowance.
Once sewing is completed, use pinking shears go cut off excessive fabric. *Typically I would do this before I even start the project, but didn't this time.
Turn inside out, place pillow form inside, and you are finished!