Three years ago I wrote a 341 words article about internet marketing placing it on one of my blogs: word count 341 competition 13.000.000 it´s still ranking n° 1 that said, today I keep my (commodity) rule; around 350 words for a blog post (if that's what it needs to say what I have to say), mixed with around 1000-1200 words (10-15%) articles. This works well on the sites I write articles for.
It depends on the topic. You should keep writing until it provides the intended information for your readers.