The rim is exactly 10 feet from the ground for junior high, high school, NCAA, WNBA, NBA, and FIBA. Rims are 18 inches in diameter at all levels of play. At each of these levels, the backboards are likewise the same size. A standard backboard is 6 feet broad and 42 inches (3.5 feet) tall. Some backboards are made of glass but most are made of plastic. The floor is supposed to be flat, but there are always bumps and dips in it. The height of these irregularities varies by sport and venue. In basketball, the average height of a basketball court is 10 feet 6 inches; in tennis, it's usually around 12 feet; and in ice hockey, it can be as much as 20 feet. The difference between the highest point on the floor and the lowest point should be about 2 inches. If it's less than that, you're playing on an uneven surface or there is something wrong with your court. If it's more than that, try to get someone to smooth out the floor before you play your next game. You should never have to worry about damage to the floor while it's wet! Courts are also graded based on how hard they are. If you know any kids who play basketball, they probably have an opinion on which courts are the hardest and which are the softest.