Basketball sizes vary depending on the league or governing body for a particular basketball game. Basketballs are measured by circumference, inflation pressure or weight. According to USA basketball, balls should be made of leather or synthetic leather. A properly inflated ball of the correct size for level of play is important to ensure safety and skill development.
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The NBA and WNBA
NBA basketballs, according to USA Basketball, are 29.5 inches in circumference while the WNBA's basketballs have a maximum circumference of 29 inches. Both should be inflated to between 7.5 and 8.5 pounds per square inch.
NCAA men's basketballs have a maximum circumference of 30 inches, and the seams must be no wider than 1/4 inch, with a weight of approximately 22 ounces. NCAA women's basketballs are a maximum of 29 inches in circumference, with a maximum weight of 20 ounces and seams no wider than 1/4 inch.
International basketballs for men's play have a circumference of 78 centimeters -- 30.7 inches -- and are referred to as size 7. In women's international play, the maximum size is 74 centimeters (29 inches), size 6. When dropped on the playing floor from a height of 1,800 millimeters (6 feet) the ball should bounce to a height between 1,200 millimeters and 1,400 millimeters (47 to 55 inches), measured to the top of the ball.
Most youth or junior basketball leagues for players 8 years old and above will use a collegiate or NBA size basketball. For players younger than 8, smaller sizes can be used. Most youth leagues will use basketballs between 28 and 29 inches in circumference.