Bought size 2/3.  My son is just shy of 2yrs old (23months!), 27lbs, and 3ft tall.  This costume fit him almost perfectly although still baggy enough in the legs and sleeves that he may still be able to use this costume next year if he wanted to.  Wow we got SO many compliments while trick-or-treating and the best part is, he seemed quite comfortable wearing this and didn't complain or tug at it at all the entire night!  I think it helped also that we had him in his pajamas underneath (which didn't show through the material) since the weather was cold up in the mountains. Isn't made flimsy or cheap looking like a lot of the stuff I saw at Target, Walmart, and even specialty costume stores.  Really really happy with this purchase!