<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (May 2013) (Learn how and when to remove this template message) </Td> </Tr> <P> A backboard is a piece of basketball equipment . It is a raised vertical board with an attached basket consisting of a net suspended from a hoop . It is made of a flat, rigid piece of, often Plexiglas or tempered glass which also has the properties of safety glass when accidentally shattered . It is usually rectangular as used in NBA, NCAA and international basketball . In recreational environments, a backboard may be oval or a fan - shape, particularly in non-professional games . </P> <P> The top of the hoop is 10 feet (305 cm) above the ground . Regulation backboards are 72 inches (183 cm) wide by 42 inches (110 cm) tall . All basketball rims (hoops) are 18 inches (46 cm) in diameter . The inner rectangle on the backboard is 24 inches (61 cm) wide by 18 inches (46 cm) tall . </P> <P> In professional and most higher college settings, the backboard is part of a portable stanchion that can be moved out of the way in other sports, though in most high schools and examples such as Stanford University's Maples Pavilion, backboards are mounted as part of a suspended system using ceiling joists to support the goal and allow them to be put out of the way in the ceiling when not in use . </P>

What is the diameter of the basketball rim