Chicken Boy's Classic T is short-sleeved and 100% cotton (pre-shrunk) Beefy Ts in sizes for littler kids (2T, 3T, 4T), and the “youts.” So, a small is marked for ages 6-8, medium for ages 10-12, and large for ages 14-16. A large seems pretty close to an adult S. We have found that kids looove Chicken Boy (like when we were filming Chicken Boy: The Movie along the Venice boardwalk, a bunch of kids followed him around and tugged at his shirt and wanted to talk to him).