What is quality score?
Quality Score is Google Ads' 1-10 estimate of how relevant a keyword, ad, and landing page are to a searcher, built from expected click-through rate, ad relevance, and landing page experience. It directly affects both ad rank and cost-per-click, but it's a point-in-time diagnostic snapshot, not a metric to sum or average across a date range the way spend or clicks can be.
Google computes Quality Score per keyword, from three components it discloses at a Below Average / Average / Above Average level (not the raw underlying number): expected clickthrough rate, ad relevance, and landing page experience. A low score on any one component raises effective cost-per-click for that keyword, since Google's ad rank formula factors quality alongside bid.
The most common misuse of Quality Score is treating it like a flow metric: summing it, averaging it across a reporting period, or plotting it as a trend the way you would spend or conversions. It's a stock metric, a snapshot of current estimated relevance, and the only valid read of it is the latest value per keyword, not an aggregate over a date range.
Meta's closest equivalent is its ad relevance diagnostics (quality ranking, engagement rate ranking, conversion rate ranking), reported the same way, relative to other ads competing for the same audience, not as an absolute score, and with the same rule: read the current ranking, don't average it over time. On both platforms, a below-average score is a genuine signal worth investigating (creative fatigue, landing page mismatch, poor targeting fit), but it should never be the sole justification for pausing or rebuilding an ad on its own, without checking the ad's actual within-group conversion rate and cost.