Mary Dobson offers these simple instructions on how to make your own pleated cushions. Pleated Cushions
Disappearing marker pen
Measure the cushion form and add 1 inch all around for seam allowance and cut one layer for the cushion back to this size.
Determine the number and size of pleats required. In this example, the cushion is being made with four pleats, each 1 inch deep. For each pleat in this size, add 2 extra inches to the length of the cushion front fabric in addition to the 2 inches for the seam allowance. The width of the front fabric layer will be the same as the already cut back layer. Tip – Cut this section several inches larger to begin and trim down to exactly match the back layer once all of the pleating has been finished.
Working on the front side of the fabric, determine the placement of the top pleat and move forward 1 inch. At this placement point, mark a straight line across the width of the fabric with the fabric marker. Repeat every three inches. Be sure to keep the line perfectly parallel with the top cut edge.
Move an ironing surface and fold the fabric wrong sides together along each marked line and press. Pin the secure and move to sewing machine.
Pin to secure and machine stitch 1 inch in from the pressed edge. Tip – the fabric may want to creep along as you sew so pinning is important but you also can alternate the direction you begin sewing from.
Move back to the ironing surface and hand press the pleats in the direction you would like them to sit and then turn pleats down on the board and steam press for the back.
Place the cushion back layer right sides together with the pleated front and trim as needed to make both layers the same size.
Machine stitch the two layers together and apply zipper to bottom edge if desired.
Finish and trim seams and flip right side out. Press and insert cushion form.
For intersecting pleats add calculated width and length to front section. Press and stitch all of the pleats in either the length or the width and then work in the alternate direction.
For butterfly pleat, press and stitch the pleats in place and then pull back the center of the pleats and hand or machine stitch to secure.
Here is the link to Video Pretty In Pleat - CityLine