I remember wondering how high the step was that Cathe was using (she's 5 '2", I think) and I stopped the tape to count. I think it was 16". When in doubt, I'd say start at a higher level (18"or 16", then as you get stronger in that range of motion, go a bit lower--I'm just a stickler for safety, and the idea of "bouncing" or "falling" onto the seat with a weight on one's back is not a pleasant prospect. Even if it doesn't hurt if you do it, the cumulative trauma would probably do bad things to your spine.