What goes into it
Google bases it on three parts: expected click-through rate, ad relevance and landing page experience. Each one is rated as above average, average or below average.
How it's meant to be used
Google describes Quality Score as a diagnostic tool. The live ad auction uses its own real-time quality signals, so the score is best used to spot which keywords need better ads or pages.
Why it affects costs
Ads that are more relevant and useful tend to win better positions at lower costs. Improving the things Quality Score measures usually lowers what you pay per click over time.
Why Quality Score matters
Low Quality Scores often point to wasted money: ads that don't match the search, or landing pages that don't deliver what the ad promised. Fixing those issues helps both your costs and your conversion rate.
Matching the page to the promise
A dental practice sent ads for 'emergency dentist' to its general homepage, and the keyword's landing page experience was rated below average. A dedicated emergency page with hours, a call button and same-day booking improved the rating and lowered cost per call.
Common mistakes
Chasing the number itself
A higher score is a means, not the goal. Focus on profit and conversions, and use Quality Score to find problems.
One ad group for everything
Mixing unrelated keywords in one ad group makes ads less relevant to each. Group tightly related keywords with ads written for them.
Ignoring the landing page
Better ad copy can't fix a slow or off-topic page. Make sure the page matches the search and loads fast on phones.