Remove the chair's seat cushion. If it is attached to the chair, turn the chair upside down and remove any screws with a screwdriver.
Remove the staples from the cushion with the screwdriver.
Place the cushion upside down onto a sheet of plastic. Fold the sheet around the cushion, pulling all sides firmly so that the plastic on top is wrinkle free and so that each corner is interlocking.
Staple each interlocking corner together, and remove the cover from the cushion.
Sew the folded corners together with a 7/8 inch seam using a sewing machine.
Remove the place-holding staples from each corner and slip the sewn cover over the cushion again.
Place the seat onto the chair and reassemble it using the screwdriver and removed screws.