Page Authority vs. Domain Authority
Page Authority (PA) scores one single page's likely ranking strength on a 0-100 logarithmic scale, pulled live from Moz's index, while Domain Authority (DA) scores the entire domain the page sits on. A page can carry a high PA even on a domain with only a modest DA, if that specific page has earned strong links of its own - and the reverse is common on large sites, where most individual pages sit well below the domain's overall DA, since only a handful of pages (often the homepage) concentrate most of a site's link equity.
What the three numbers together tell you
This tool checks three figures at once for any URL: Page Authority, the domain's overall Domain Authority for context, and Spam Score - Moz's estimate of how closely a site's profile resembles sites that have been penalized in the past. Looking at all three together gives a fuller picture than any single number: a page with high PA on a domain with a high Spam Score, for instance, is a very different situation from the same PA on a clean domain.
Why PA isn't a ranking guarantee
Page Authority is a comparative, link-based strength signal built from Moz's own index - it is not a direct Google ranking factor and doesn't account for content relevance, search intent match, page experience, or any of the dozens of other things Google's actual algorithm weighs. Use it to compare the relative link strength of competing pages, not to predict exactly where a page will rank.
Practical uses
Comparing two of your own pages to see which has attracted stronger links, sizing up a specific competing page before trying to outrank it, or checking the authority of a specific article or product page you're considering linking to from your own content.