As far as I know (as I don't use an exercise ball any more. Other than for "drive way" basketball using our large trash can with my grown son's once in a while), these are the sizes they make:
55 cm - 4'11" - 5'4"
65 cm - 5'5" - 5'11"
75 cm - 6'0" - 6' 7"+
The "primary" purpose of a stability ball, is to put you in an unstable environment. Additionally, while you are performing an exercise, the body is constantly making small adjustments with the postural muscles, abdominals, gluteals, and leg muscles because of this instability.
Hope this helps.
Chillen
