Calculate the length measurement of the footstool from the floor on the long end of the footstool, up the side, over the top and down the opposite side to the floor. Add 1 inch to the measurements for the hem.
Calculate the width measurement of the footstool from the floor on the short end of the footstool, up the side, over the top and down to the floor on the opposite side. Add 1 inch to the measurement for the hem.
Cut out a piece of fabric using the two measurements taken. The fabric will be either a square or rectangle, depending on the shape of the footstool.
Drape the fabric over the footstool so the right side faces down and the side fabric drapes evenly. Pull the corner points out and pin the fabric along the edge of the footstool to mark the sewing location. The excess fabric on each corner will be in the shape of a triangle.
Remove the fabric from the footstool and sew along the pinned marking. Remove all pins and cut off excess fabric, leaving a 1/2-inch salvage. Seam finish the edge with a zig-zag or serged stitch.
Turn under the bottom edge 1/4 inch to the wrong side of the fabric. Pin or iron the fold to hold it in place. Fold over another 1/2 inch to create a hem. Secure the bottom hem by sewing close to the inside edge.