But there's more, and this is why novels are long: - not too long, not too short, but of a certain length-- of a certain magnitude, as Aristotle puts it.

但是当然还有很多别的东西，要不这本书也不会那么长：,不是太长，但也不短，刚刚好能说明清楚问题的长度-,亚里士多德这么评价。

耶鲁公开课 - 文学理论导论课程节选

How long" can be used in a question and it refers to a length of time or a length of distance.

How long” 句型用于问句中，用来询问时间或距离的长短。

How long课堂 - SpeakingMax英语口语达人