Standard Pillow Sham Size
A standard bed pillow is 20 inches wide by 26 inches long. A simple pillow sham would be just slightly larger -- 21 inches wide by 27 inches long. Some pillow shams have a flange (an additional amount of fabric that frames the pillow) or ruffles around the perimeter. In this case, a pillow sham for a standard pillow would be about 27 inches wide by 33 inches long, though it could vary depending on the exact design of the sham.
To make a simple pillow sham for a standard size bed pillow, cut out a rectangle of fabric that is 57-1/2 inches long and 22-1/4 inches wide. At each of the shorter ends, measure, press and pin a double ¼ of an inch hem. Do this by folding ¼ of an inch of the fabric to back, pressing with an iron, and folding the ¼-inch hem to the back one more time. Press, pin and sew. Lay the fabric on your work surface with the right side (the side you will see when the pillow sham is finished) facing upward. Fold over the two ends of the fabric so they overlap by 3 inches in the center. The wrong side of the fabric will now be facing upward. Press and pin. Sew along the two sides of the pillow sham, making your seam 5/8-inch from the raw edges. Turn the pillow sham right side out and insert the pillow through the opening in the back of the pillow sham.
To make a pillow sham for a standard bed pillow with a 3-inch wide flange on all four sides, cut out a rectangle of fabric that is 63-1/2 inches long and 28-1/4 wide. Follow the directions for making a simple pillow sham, but do not insert the pillow. After you have turned the pillow sham right side out, press it flat paying particular attention that the edges are straight and extended as far as they can go. Mark on the back of the pillow sham with a fabric marker a rectangle 3 inches in from the edges of the pillow sham. Sew around this rectangle to create the flange. Now insert the pillow.
Any pillow can be covered with a pillow sham, from throw pillows on the sofa, to bolster pillows for back support, to floor and other large pillows. The basic directions given above can be used, or you can make fancier pillow shams with ruffles, sewn or ironed-on embellishments and more elaborate closures.