We use king size pillows, but we only have full size pillow cases. I decided to extend those to the needed length, and so went out and picked up quilt fabric to add to the pillow cases. I chose 'fat quarters' that JoAnn's has for sale and simply matched them to the pillow case I'd brought with me.
First I ironed the pillowcases inside out, making sure the seams were flat. Then I cut off the seam on the narrow end, where I will add my fabric.
I get the fabric and make sure it's folded so that I have enough length (it works one way, but not the other, due to the way it's cut). I iron it that way and then use my quilting supplies to trim it square.
I'm using french seams on this project, as I don't have a serger.
I hem one short end of the quilt fabric, creating a finished seam, and then turn it inside out.
The pillow I have right side out. The quilt fabric goes inside the pillow, right side facing in. I match up the seams - the side seam on the pillow with the short one on the quilt fabric. Next, sew down both long sides, starting from the seams and going down. Don't finish them, just stitch the pieces together. I leave the bottom (the long seam) open while I do these sides.
Once both sides are done, pull the quilt fabric out of the pillow and sew shut the open end of the quilt fabric. You want to make this seam just a bit longer, say 5/8", than the outside edge of the pillow. This is your seam allowance to finish the seam and hide the fabric edges.
Trim the extra fabric on all the seams down to about 1/8".
Turn the pillowcase inside out, and tuck the fabric quilt back inside the original pillowcase. Sew the seams from this side to create the french seam on the inside. The frayed edge of the fabric should be completely hidden inside the seam. When the side seams are done, pull the quilt fabric out again and finish the last seam.
Enjoy your new pillowcases!
Two pillowcase pairs I made this way. The crochet afghan was made for us by my mother.