Remove the seat from the stool base by unscrewing the hardware and pulling off the seat.
Lay the seat on top of a large piece of paper and trace around the outside edge for a pattern.
Add 3 inches to each side of the stool, or if the seat is circular, add 3 inches around the entire circle. Use the pattern to cut a piece of upholstery fabric.
Cut a piece of upholstery foam, 1-inch thick, using the tracing for the exact size of the seat.
Set the fabric on a sturdy surface so the top side faces down. Lay the foam in the center of the fabric and set the seat on top of the foam so the top side faces down.
Secure the fabric and cushion to the seat by pulling a section of the excess fabric to the under side of the seat and stapling it in place. Repeat this process around the seat, making sure you flip it over to verify the fabric remains smooth and not puckered from pulling.
Attach the seat to the stool with the hardware you removed.
Flip the stool on top of a large piece of paper so the legs are in the air if you cannot remove the seat. Trace around the outside edge to make a pattern.
Increase the pattern evenly by 3 inches so there is extra fabric for attaching to the seat.
Cut a piece of upholstery foam, 1-inch thick, to the exact size of the seat.
Lay the fabric so the top side faces down; invert the stool and set the seat on top of the foam so the legs are sticking upright if you cannot remove the seat.
Pull sections of fabric to the bottom of the stool seat and attach the edge with a staple gun. Continue this process around the seat of the stool to secure the fabric.