Length should allow a free pendulum stroke and stable bridge. Height matters, but arm length, stance and cue-ball distance matter too.
Check the room at the extremes of your stroke so the butt does not hit a wall. A short cue can solve a tight spot; an extension can help reach when the joint is compatible.
Measure full cue length and each section, especially for case fit. A repeatable test at the table beats a generic height chart.