Google cannot measure “quality” directly, so it approximates it through measurable proxies. There is no quality meter that reads a page and returns a verdict; instead the system infers quality from signals it can actually compute. The honest framing is that quality is inferred from proxies rather than read, and knowing the proxies is more useful than either imagining a direct score or falling back on the vague advice to “just write good content.”
The proxies fall into a few recognizable groups. Links, both how many relevant sites reference a page and the authority behind them, stand in for whether others find it worth citing. Aggregate user-behavior signals, the patterns across many searches in how results are engaged with and whether searchers seem satisfied, stand in for whether the page met the need. Relevance and coverage match, how well the content answers the query and how completely it covers the topic against what the SERP demands, stand in for usefulness. Content and entity signals, the topical depth and the recognizable people, things, and concepts a page is associated with, stand in for substance. And page experience, loading behavior, stability, and mobile usability, stands in for whether the page is pleasant to use.
The reason this matters is that you cannot optimize a thing that is not measured, but you can improve every proxy that stands in for it. “Quality” is the outcome those signals are trying to estimate, and a page that genuinely earns links, satisfies searchers, covers the intent fully, demonstrates real substance, and loads cleanly is one the proxies will read as high quality, because that is what the proxies were built to detect. The proxies are estimates and they shift, so treat the exact weighting as something to watch rather than a fixed formula.
To act on this, stop chasing an invisible quality score and improve the measurable proxies it is inferred from: earn relevant links, satisfy the searcher’s actual intent, cover the topic completely, build genuine topical substance, and keep the page experience clean. Improve the proxies and the inferred quality follows, because the proxies are all Google has to read.