Measure the length of your mattress and add 1 inch. This is measurement A.
Measure the width of your mattress and add 1 inch. This is measurement B.
Cut a rectangle from muslin that is equal to the measurements you found in Steps 1 and 2.
Hem the short sides of the muslin rectangle using a sewing machine. This is the decking of the bed skirt.
Measure the distance from the top of the box spring down to the floor and add 1 inch. This is measurement C.
Cut two rectangles of fabric using measurements A and C. This is the fabric that will be visible on your bed skirt.
Hem both short edges and one long edge of these rectangles of fabric using a sewing machine.
Match the long unfinished edge of one fabric rectangle to one long unfinished edge of the decking, with the patterned or right side of the fabric facing inward, and pin them together.
Sew the unfinished edges together, leaving ¼ inch between the seam and the edges of the fabric.
Repeat steps 8 and 9 for the other rectangle. Spread the decking over the box spring, allowing the sides of fabric to hang down. The patterned or right side of the fabric should face out.