Measure the length and width of the chair to figure out how much fabric you need. Add 6 inches to allow for attaching the fabric to the underside of the seat.
Take the diameter measurement of the stool seat. Measure the depth of the stool as well and then add an additional 6 inches for attaching the fabric to the underside of the stool. Cut your fabric to the necessary measurements.
Remove the drop-in seat from the chair. If the stool has a removable seat, take that off as well. Use a screwdriver if necessary to remove the seats.
Lay your fabric out on a work surface with the right side of the fabric facing down. Center either the stool or the chair seat on the fabric.
Pull the fabric up at the center of the sides of a square seat and staple the fabric to the underside of the seat. Pull the fabric up at one point and then directly across from it on a circular seat. Repeat on the circular seat two more times to make four points.
Work from the center staples out to the corner on a square seat, pulling the fabric tightly and stapling in place. Work from staple to staple on the round seats. Keep checking the fabric on the top of the seat to make sure it is pulled tightly without leaving wrinkles.
Trim any excess fabric once you completely staple the fabric in place. Trim the fabric about 1 inch past the staples.
Replace the seats in the chair frame or on the top of the stool.