The diameter of a men's basketball is around 9.5 inches, while the circumference is 29.5 inches. At the high school level in the United States, the ball used in play is typically about 98% air and 2% rubber. A high school basketball needs to be inflated to about 10 pounds per square inch (psi) for play. Basketballs come in many sizes and shapes but generally fall into three categories: college, junior college, and high school. The size of a basketball depends on the category it falls under. For example, a high school basketball is usually between 7 and 8 inches in diameter, whereas a college basketball can be as large as 10 inches. There are also juniors college basketballs that are approximately 9 inches in diameter. These balls are designed for young players who are just beginning to develop their skills so they don't have to be as heavily weighted as older balls to be played well. Finally, there are pro basketballs which can be up to 10 inches in diameter. These are heavy balls that are designed for use by very skilled players during game situations.