There is no definitive answer to this question as it depends on the type of blog post, the purpose of the excerpt, and the tone of the blog. However, a general guideline would be to keep blog excerpts under 500 words.
This will help to keep your readers engaged and allow them to see all of the key points of the post without having to read the entire article. Additionally, shorter excerpts will also make it easier for you to sprinkle in additional information or images that might be important for your readers to see.
When writing a blog post, it is important to keep in mind the tone of your writing and the purpose of your post. For example, if you are writing a post about gardening tips, then a longer excerpt would be appropriate. On the other hand, if you are writing a post about breaking up with your significant other, then a shorter excerpt might be more appropriate.
Ultimately, it is up to you as the author how much detail you want to include in your blog excerpts. Just remember that shorter excerpts will help to keep readers engaged and provide them with all of the key points while still providing enough information for them to form an opinion.