The size of the volleyball you should buy depends on the age group and skill level. Standard sizes for indoor volleyball include:nn- Official Size (Adults): Circumference of 25.6 u2013 26.4 inches (65 u2013 67 cm), weight of 9.2 u2013 9.9 ounces (260 u2013 280 grams).n- Youth Size (Ages 12-18): Circumference of 23.6 u2013 24.8 inches (60 u2013 63 cm), weight of 8.0 u2013 8.8 ounces (220 u2013 250 grams).n- Junior Size (Ages 8-12): Circumference of 22.0 u2013 23.6 inches (56 u2013 60 cm), weight of 7.4 u2013 7.75 ounces (210 u2013 220 grams).nnIt's important to choose the appropriate size to ensure proper game play and skill development.