An athletic cup is meant to be worn over a man's testes and scrotum to protect the delicate tissue during sports. The cup needs to be at a depth that closely but comfortably cradles the entire genital area. The accompanying jock strap should fit comfortably both at the waist and leg straps.
Typically, the cup size correlates to the size of the man's body. A youth may wear a cup with a 1 3/4 to 2-inch depth. However, a man probably needs from 2 1/4 to 2 1/2 inches of depth. The only way to know for sure is to try the cup on over shorts or, better yet, underwear. It should fit snugly with no pinching or excess room.
The jock strap is an undergarment with a waistband and a pouch connected in the back with straps. The hard cup goes inside the front pouch. The size of jock straps corresponds to the waistband size, with the pouch and straps getting larger according to the size.
Non-contact sports such as running, basketball and rollerblading might necessitate simple supporters or the jock strap worn alone. Contact and high-impact sports, such as hockey, football and baseball, require a hard cup. Depending on the desired level of protection, an athletic cup inside a jock strap can be worn over briefs or even compression shorts.