What is domain authority?

Moz coined Domain Authority, which is why the phrase is often used as though it were universal. Ahrefs calls its equivalent Domain Rating and Semrush calls it Authority Score. They are built from different link indexes with different formulas, so the same site can score 40 on one and 55 on another and neither is wrong. Rankizo publishes no score of its own: it reports the authority rank its data provider returns, and can add Ahrefs' Domain Rating to each row where you want that specific number.

All of them are logarithmic. Moving from 20 to 30 takes a fraction of the links that moving from 60 to 70 takes, which is why a new site's score climbs quickly at first and then appears to stall.

Comparing, not measuring. The score is useful when you put two sites side by side — is this prospect stronger than that one, are the pages ranking for my target query far above me or within reach. That is a judgement it supports well.

It is not useful as a target. Nothing in Google's systems reads it, so a page does not rank better because the number went up; the number went up because the things that do affect ranking improved.

It is a whole-site average, so it says little about the page you care about. A weak page on a strong domain routinely loses to a strong page on a weak one, and a domain-level score cannot show you that.

It is also gameable, which is why scores get sold. A site can lift its authority score with links that no search engine counts, and the number moves while the traffic does not. If you are evaluating a domain to buy or a site to be linked from, look at whether it has organic traffic before you look at its score.

For a page you want to outrank, count the referring domains pointing at that specific page. That single number predicts far more than either site's domain score.

For a site overall, read organic traffic and the number of keywords it ranks for. A domain with a score of 70 and no traffic has a link profile and nothing else.