What is the size of a basketball backboard? Per NBA regulations, the dimensions of a basketball backboard are 6 feet wide by 3 ½ feet high. The backboard is marked with a 2-inch white rectangle that is centered behind the ring; the rectangle's outer dimensions are 24 inches wide by 18 inches high. The basket itself consists of a metal ring with an 18-inch inner diameter and a white cord net that is 15 to 18 inches long.