After measuring the square dimensions of the pillow, I added 1" to both dimensions and used these dimensions to cut the front of the pillow. For the back of the pillow, I added 1" to the width across the pillow and 5" to the height to account for the overlap in the envelope fold. The two pictures below show the front (top photo) and back (bottom photo).
I had also purchased this spirited modern home decor fabric by Waverly, Wild Life in 3 different colors. At first, I wasn't sure what I was going to do with it, but after making my first set of pillow covers, I thought that making some pillow covers with the Wild Life fabric would be a sure way to add some fun color to a room. The colors all look so great together and definitely will brighten any room! I added a top stitch detail around the edges to give them a little extra style. The throw pillow covers shown below are made to fit 16"x16" pillow forms and can be purchased in my Etsy shop in the for the HOME section.