Wash the tightly woven fabric. This will prevent any further shrinking after the slip cover has been made to fit the platform rocking chair.
Hold the fabric against the left side of the rocking chair with the back of the fabric facing out and mark the fabric with chalk along the outer edges. Remove the fabric, add a few more inches around the entire perimeter with the chalk and cut out the shape. Repeat this process for the right side and the back of the chair. Place fabric along the seat and backrest of the chair, trace around the edges, add a few inches and cut. Place fabric along both armrests and repeat the process.
Place the pieces against their respective sides with the back of the fabric facing outward and pin them all together where you would like them to be sewn. If you want to have a loose cover on your platform rocking chair, pin the sections to hang loosely.
Sew the sections together along the pins with the back of the fabric facing outward.
Remove the pins, cut off the excess fabric from the seams and turn the entire cover inside out.
Place the cover over the platform rocking chair to cover it.