This is a difficult question to answer because it depends on many factors, such as the topic of your blog post, the competition for that keyword, and how well your blog post is optimised. However, as a general rule, a blog post should be at least 300 words in order to be effective for SEO. If you can make your blog post longer, it will likely be even more effective. However, don't sacrifice quality for quantity – a shorter, well-written blog post is always better than a longer, poorly written one.