Measure the length and width of your patio cushions. Add 1 inch to each measurement and cut two pieces of outdoor-suitable fabric to match each of these measurements.
Pin two matching pieces of fabric together with the right sides facing, placing straight pins approximately every 2 inches around the perimeter of the fabric pair. Repeat this step for all pairs of fabric pieces.
Remove one pin at a time and glue the fabric pieces together along three sides. Place a line of heavy duty fabric glue or no-sew stitch glue along the edges of the fabric, 1/2 inch or less from the cut edge. Allow the glue to dry.
Turn the fabric pieces right side out so they form a pocket. Slide the patio cushions into each pocket.
Make a 1/2-inch fold in the fabric on either side of the open pockets; fold toward the inside of the pillow cover. Glue the folded edges onto themselves and pinch them down with clothespins or chip clips until they dry.
Place a line of glue along the fold on one side and press it to the other piece of folded fabric to seal the pocket closed. Pinch it shut with clothespins or chip clips and let the glue dry. Remove the clips before using the patio furniture.