Turn the sling-back chair around so that the back of the fabric is toward you. The fabric has been looped over rods at the top and the bottom of the chair and then sewn to itself. Use a seam ripper to pick out the seams from the fabric around the top and bottom rods. Remove the fabric from the chair.
Lay the fabric on the butcher paper and trace the outline with your pencil. Remove the fabric and use a ruler to make another line 1 inch outside the outline to allow for seam allowance. Cut out the butcher paper pattern on this second line.
Lay the butcher paper pattern on the fabric and pin it in place. Cut out the pattern piece from the fabric. Remove the pattern piece and pins.
Place the fabric right-side down. Fold down each side ½-inch and iron. Fold down an additional 1/2-inch and iron. Pin the fold into place. Thread your sewing machine and sew around all sides using a straight stitch and a 3/8-inch seam allowance. Remove the pins.
Position the fabric on the chair. Loop the short top edge over the top rod of the chair and bring it down the back 2 inches past the rod. Pin it into place. Loop the other end of the fabric over the bottom rod. Bring the fabric up 2 inches past the rod and pin it into place. Adjust the fabric until it fits the chair as you wish.
Cut a long piece of heavy-duty upholstery thread and insert it through the upholstery hand-sewing needle. Pull the thread until the ends meet and tie a double knot in the ends of the threads.
Sew the pinned edges of the fabric around the top rod into place with the needle and thread. Make your stitches as short as possible so that they are nearly invisible. Use a thimble if necessary to help you push the upholstery needle through the heavy fabric. Tie a triple knot in the ends of your threads when done with your seam. Remove the pins. Repeat this step with the fabric around the bottom rod.