I got this costume for my 9 year old boy, who is avg height/weight.  I ordered a large and it BARELY fit.  The costume is adorable, and the material is really nice, the satin pants, the robe, very nice.  However, he'll outgrow it in 3-5 months.  The hat ... the hat was ridiculously small, it no wear near fit his head.  I ended up cutting the hat up a seam so it would fit for his show.  Its really unfortunate that it ran so small.  So if you want this adorable costume to last (and fit), go larger than you want.

My son is about 54 inches, about 60 lbs