Short answer: As long as they need to be — and not a single word longer.

Long answer:
It seems that blog posts between 2,000 and 4,000 words tend to rank best on Google. So if you’re writing primarily for search engines, that’s a good target range. And it’s the reason the pro-bloggers write primarily posts of that length.

Of course, sometimes the topic naturally determines how long your article should be. If you’re writing an opinion piece titled “Is Die Hard a Christmas movie” you could end it in a single sentence:

Yes, and Yippee-Ki-Ya, motherfucker.

But if your article is titled “How to Write a Book,” even 4,000 words might not be enough.

My approach is to write for readers first, myself second, and search engines last. That means I focus on giving the reader exactly what the title promises — as clearly and concisely as possible. Adding unnecessary words or paragraphs just to please Google is counterproductive. So I keep things short and simple.

Take Derek Sivers, for example. I like his blog because he follows the same philosophy. Some of his posts are shorter than 300 words, yet they still deliver great ideas.

For the real-time biography blogging niche I’ve defined for my writing on this site, my goal is to give you a quick look into my work and progress that usually contains one idea at a time. Hence, short posts are totally fine, and even better than 1,000 words of rambling.

On the first day of every month, I publish a longer post titled “Progress Report.” It’s already grown to about 1,000 words per post — and naturally, it’ll become longer over time as my Author in Progress project develops.

However, posts like the one you’re reading right now usually range from 300 to 500 words. And I believe that’s enough to deliver what the title promises.

You tell me if I’m wrong.