It depends on how tall you are and how tall the Fanny Lifter is, I would say. I am 5'8" and use a 17" step for the High Step routines. Women Cathe's size probably need 14". The high step is used in the new workouts (HSTA etc) and in Boot Camp, ME, Leaner Legs, PS Legs, Legs and Glutes,...I think that's it but I'm sure someone will correct me.