What is the best length for a post?

I’ve wondered about the answer to this question myself.
I’ve read plenty of studies that purport to tell what the best length of a blog post is:
Here’s Buffer’s infographic and analysis.
Here’s The Write Practice on different types of blog lengths for different purposes.
Here’s Quicksprout’s data-driven answer for blogs.
I think the answer is different for different people. For me, I discovered it depended entirely on how soon my audience was reading the post.
If I’m writing for someone to read today, and I want them to come back to read tomorrow’s post – that is, if I’m building an audience of repeat readers (who I can sell advertising to? products to? etc), then shorter seems to be better.
I tried to keep my “inspiration” posts shorter, for that reason.
Then I realized most of my posts aren’t written for people reading today.
More people come to a blog post after I’ve published it – months or years later – than came on the day it was written.
And the people who came to the post were searching for an answer to a question or insight into a topic, and thus had a longer attention span and craved more detail. Because that’s who I’m writing for, I try to provide it.
That also made me more willing to go back and add additional details later, or correct or refine a post after I’ve written it. And it’s also why I don’t write much about topics that have a limited lifespan (for that, I use social media).
It led me to start using non-public blog pages to organize ideas around a topic, and then start turning those ideas into blog posts (like writing specific bits of an outline). I tackle different elements of the outline at different times, not exactly in order–but eventually I’ll make the topical page public as well.
Since I began tilting in this direction, I’ve been seeing a consistent increase in the number of page-views, too: my visitor count and page views have doubled. So, that’s a certain measure that I’m successfully serving people’s information needs.