Page Authority (PA) is a score that predicts how well a certain page ranks on search engine results pages (SERP). Page Authority values vary from 1 to 100, with higher values that match better ratings. It is a score developed by Moz.
Page Authority is calculated using data from our web index and takes hundreds of criteria into account. Domain Authority employs a machine learning model to determine the formula that best correlates with ranks across the hundreds of SERPs against which we forecast and then generates Page Authority ratings based on that specific calculation.
With a standard 100-point scale, the PA score will constantly fluctuate, not a fixed number. PA scores increase rapidly between 20 and 30 but are difficult to achieve between 70 and 80. The usage of Page Authority as a comparative metric (rather than an absolute, tangible score) for searcher results is best done and which pages may have more powerful or more relevant links than other sites. Since it's a tool of comparison, a "good" or "bad" authority score is not necessarily available.