The basic answer: as long as they need to be to say what you have to say.
Now let’s get into some more depth.
- There is no hard and fast rule. Old-school marketers will tell you that long sells, by which they mean that long sales copy typically converts better than short sales copy. Your blog isn’t sales copy, so that’s not really relevant. Other people will tell you that people don’t read any more. This is demonstrably false. People read a lot, especially on the internet. Some folks spend hours browsing through Facebook, reading things.
- People read differently online. Lots of scanning takes place on web pages. First, most people will scan before they commit to reading. They’ll scan in order to decide whether or not to stay and read your post. Then there are folks who are scanning for a particular piece of information, often the phrase they saw out on the search results page before they clicked through. You can use bulleted lists and headers to make your page more scannable. You can also break the page up from a design standpoint for the same purpose, using space and color to help visitors catch the main idea quickly.
- People aren’t all the same. I rarely watch videos online without some specific reason to do so (like I’m watching a movie, or the text under the video convinced me to, or someone recommended the video). I like to control the speed at which I get information, and you can’t really scan videos effectively. Rosie rarely reads a page online — she’ll always pick a video. Since you probably can’t predict your audience’s preferences, your best bet is to mix it up. Have videos, text, infographics, pictures, and interactive elements (search boxes, links to additional information, calculators and quizzes all count).
- You don’t have to be consistent. Long posts on some days and short posts on others are fine, assuming they’re all high quality. If you have a certain style that lends itself better to a shorter format or a longer one, honor that. Otherwise, your blog doesn’t have to have a certain word count each day.
- Never pad. Anything that has been written only so that you can take up some space will not be worth reading. You have a point to make. You need to support that point. You need enough detail to answer your reader’s questions about the point you’re making and about the supporting evidence you’re offering. You may have something amusing or some beautiful language, and those can be worth writing and worth reading, too. But anything that could be removed without changing the piece significantly, should be removed.
So just make sure that your post is tightly written and makes a point, and be sure that it’s as scannable as possible. Then you won’t have to focus on the length.