For their step ladders, Werner specifies the maximum reach height as being 4′ higher than the step ladder size. For example, to reach a 9′ height, they say you should select a 5′ step ladder. This assumes the user is 5′ 9″ with a 12″ vertical reach, and so taller or shorter...
Looking for stepladders? Find out information about stepladders. A ladder having flat steps, or treads, in place of rungs; usually provided with a supporting frame to steady it. McGraw-Hill Dictionary of Architecture and... Explanation of stepladders