Domain authority, also called site authority, is a measurement that represents how much authority a domain has to help in search engine ranking. This score and how it is calculated will vary between SEO tools and platforms, but generally it is a numerical score between 1 and 100 that is derived using website metrics that include the age of the domain, popularity by backlinks, size of the website and many other trust and SEO factors.
From PageRank to Domain Authority
The first authority score was Google’s PageRank (first released in 2000). PageRank was the industry standard used to measure the authority of a domain or website on a 10-point scale. The better the ranking, the more you would see the website rank on the first page of search results. Browser tools could be used to display a PageRank when viewing a website. By 2014, Google stopped updating PageRank tools and it was removed from web browsers. While PageRank is still used by the Google search engine, new and updated scores are not made available to the public, leaving SEO experts and web content producers and marketers to rely on third-party SEO tools to measure authority.
Moz Domain Authority (DA) Scores
Since PageRank has been removed from public eye, many SEO tools have created new tools and ways to calculate domain authority. One of the more well known implementations is the Moz version, which claims to use more than 40 metrics to calculate its Domain Authority (DA) score.