I personally started by writing of 300 words per article in back years but recently most of my posts are of 400 to 600. I find that covering a topic in a long and detailed is best for my field in attracting visitors to my blog.
Any blog contains 400 to 500 words to post, that can better describe what you want to put in front of your users, but what I prefer to write any blog for 300 to 500 words and I try to focus on the words that must be relevant to my article or blog.
Really as long as possible .
But a long article to 650 words SEO standards .
The longer your articles and quality you will be highly appreciated google