How Long Should My Blog Post Be?

The question ‘How Long Should My Blog Post Be?’ has been around for as long as blogs have. There are also numerous reasons across why we care about this question. Is it from a usability perspective? Is there a secret formula to improving reader engagement through mastering the perfect ‘not too long, but not too short’ blog post length? Following Google’s sneaky update to their link guidelines, should we still be concerned about guest posts and the editorial rules around the blogs of others?