This is a really good fit for my son who is required to wear a cup for Taekwondo. Amazon lists this product simply as a Boy's Brief though the box this came in had the following measurements listed on the back: PeeWee regular (18"-22") and large (22"-26"), Youth version regular (22"-26") and large (26"-30"). My son is 7 years old, 49" tall and 49#, and the Boy's Brief ordered in size S fits well ... though the actual label reads "PeeWee Large." Judging by this, it would seem the XS sold here corresponds to the PeeWee regular, the S to the PeeWee large, the M to the Youth regular and the L to the Youth large. Hope that helps someone out there!