How many times the heading tags should be used in a webpage?

[smartscraper]

Before we discuss this, it will be great if you refer keyword density term in SEO. 

But how does keyword density is related to the heading tags count?

[flamefox16]

Google doesn't care if you use h1, h200, or <div class="fake-heading"> - they'll still rank you by content quality. But sure, let's pretend markup matters.

Use one h1 (because "best practices" are just corporate bingo cards), then h2-h6 like a drunk guy stacking Jenga blocks - just don't blame me when your UX implodes. And for God's sake, stop abusing heading tags for CSS hаcks - that's what display: flex is for, you DOM graffiti artist.