I just checked off the last big sewing project on my nursery to do list, with only a few weeks to spare!
No detailed tutorial for this project, but the concept is fairly simple. First, I started by measuring the metal frame that holds the crib mattress, which came out to 51" x 26". The mattress is at the highest position now, but I wanted the skirt to just skim the floor when the mattress was at the lowest setting, a distance of about 10".
I cut out four panels for the sides of the skirt and one large panel for the top, adding a couple extra inches to my original measurements for seam allowances:
Two 53" x 11.5" panels for the long sides
Two 28" x 11.5" panels for the short sides
One 52" x 27" panel for the top
I hemmed the sides and bottom edges of the side panels and serged them onto the top panel. Then I sewed pom pom trim onto the bottom of each side panel.