Rhythmic gymnastics balls are available in 13cm. , 15 cm. , 17cm , 18 cm. , 18.5 cm. and 19 cm. The measurement concerns their diameter.
When it comes time to choose a rhythmic gymnastics ball you should consider several parameters. The combination of the athlete's technical level and height are what will give the first impression for the right choice. B.C. If an athlete is tall and at a high level for her age, it is recommended to choose a ball with a diameter of 18cm-19cm.
But in the end, don't forget that the final decision will be made by the person directly concerned, who should feel comfortable holding it in the palm of her hand.