Common training weights include 12 oz, 14 oz, 16 oz and 18 oz. Full-size weighted practice balls are frequently listed around 15–18 oz.
Two common sizes are compact training balls at about a 3" diameter (≈9.5" circumference) and full-size weighted practice balls at about a 9" diameter.
Weighted balls provide instant feedback on swing and throw paths, help train consistent center contact, and can help generate more power—potentially improving hitting mechanics and exit velocity.