There is not an idea that cannot be expressed in 200 words. But the writer must know precisely what he wants to say. If you have nothing to say and want badly to say it, then all the words in all the dictionaries will not suffice.I still think an idea needs between 400 and 500 words, but perhaps that is quibbling. We now have word count, of course.
Do not count a, of, the, and etc. Averaging the words in a line is O.K.
See also: On the Size of a Thought.