So if you are under 5', the extra-small ball with a diameter of 45 cm (17. 7 in) will probably work best for you.
[header] How to buy an exercise ball [title] Choose an extra-small ball if you are up to 5' (152.4 cm) tall. [step] Exercise balls are available in different sizes, based on the diameter of the ball when fully inflated. The correct ball size is selected based on your height.