Ping pong sized hollow balls, commonly used in beer pong and other party games, have a diameter of approximately 40 mm or 1.5748 inches. These balls are typically made of lightweight plastic and are designed to be easily thrown and bounced during gameplay. They are an essential component of beer pong, a popular drinking game where players attempt to throw the balls into cups of beer on an opposing team's side of a table. Additionally, these balls are often used in various other party games that involve tossing or bouncing them for entertainment purposes.