I've been on this pillow-making kick for a little while and I love being able to change the look of a room with just 45 minutes of sewing. I made these pillow covers for my friend in a single evening using this easy pattern for envelope pillows using a SINGLE piece of fabric. Here's how much fabric you need based on the size of the pillow:
12" square pillow = 12" x 30"
14" square pillow = 14" x 30"
16" square pillow = 16" x 40"
18" square pillow = 18" x 45"
20" square pillow = 20" x 50"
22" square pillow = 22" x 55"
24" square pillow = 24" x 60"
My friend, who loves wine, chose this flannel fabric with cork designs:
I have worked a lot with snuggle flannel, but never on making pillows. I am now a huge fan. It's soft, very easy to work with and looks great. Her pillows were 18" square, so I cut the fabric into 18" x 45" pieces (I made 4 identical pillows).
On each 18" end, turn the fabric under 1" using a 5/8" seam. I like to use a zig-zag stitch or other decorative stitch. Depending on the color of your thread, one of the seams will show on your finished pillow, so it's nice to make it look attractive.
Lay the piece of fabric, right side up, long side horizontal. Fold each side back toward the middle, and overlap the ends so only one seam shows. Overlap the fabrics until your fabric is 18" square. Pin the two raw ends (top and bottom in this picture). Sew those sides using a 5/8" seam.
At this point, because I was using flannel, I trimmed the seam allowances using pinking shears so it wouldn't fray. Turn the pillow cover right side out. Insert the pillow form, pushing it into the corners and then pushing into the bottom half.
And that's it! Envelope pillow covers are my preferred method of sewing pillows because you can easily change the pillow covers for a new look or season, or just to clean.