What is the radius of a full adult size NBA basketball ball?

Diameter = 2 x Radius

Circumference = π x Diameter= π x (2 x Radius)

28.5 = π x 2R

28.5 / π = 2R

28.5/3.14159 = 2R = 9.0718 OR 9.1

Radius = 9.1/2 = 4.5 inches.