There is no limit to number of words or characters in a blog post. As long as u satisfy your readers, you will be fine. Just take care of bounce rates. Bounce rate is the rate where users come from Google to your site and ta daa, they close immediately after seeing it. Google says, hmmm this is not a good post, look 90% bounce rate. Go down! Therefore, whatever the limit is, keep it good, keep it in context. What is optimum length for blog post? Write at least around 300 words for a definitive article, if you are writing an informative one, keep it at least 700 with some h2 h3 tags.