Ahrefs Rank (AR) ranks all the websites in our database by the size and quality of their backlink profiles — basically, by their DR. 

The more and higher-quality backlinks a website has, the higher its DR is, and the closer its AR is to #1.

Right now, Ahrefs Rank #1 belongs to the website with the strongest backlink profile (Facebook.com), #2 belongs to the second strongest (Twitter.com), #3 belongs to the third strongest (YouTube.com), and so on. See the full list here. 

FAQs:

Q1: "Why did my Ahrefs Rank drop if I haven’t lost any links?"

Because AR is a relative metric, even if your website didn’t lose any backlinks, other websites could gain them and overtake you in rank.

Q2: “Why did my Ahrefs Rank drop even though my backlink profile is growing?"

The same logic as above: because other websites are getting new backlinks faster than you. 

Q3: “Why did my AR drop by a million if I only lost a couple of backlinks?”

AR gets more volatile towards the lower end of the scale. 

There are only a handful of websites in the world with millions of backlinks, so it takes exponentially more effort to outrank sites at this level (Think Twitter, YouTube, etc.)

But at the very bottom end of the scale, websites tend to have few to no backlinks. If these sites get just one new backlink, that's likely enough for it to outrank hundreds or thousands of other websites.