I made my skirt essentially a size 2T around the waist. The skirt is long though, reaching about calf lenth on my toddler. I made it long on purpose. Since my older daughter is so thin it actually fits her and reaches about knee length on her. So by making it long I basically made a skirt that they could both wear. If you want it to be a true 4T, just add an inch or two in the elastic at the waist.