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What are Core Web Vitals?
Core Web Vitals are three measurements Google uses to score how a page feels to a real visitor: how long the main content takes to appear, how quickly the page responds to a tap, and how much the layout jumps around while loading. They are part of Google's ranking systems and are reported per URL in Search Console.
The three numbers
Largest Contentful Paint measures when the biggest visible element finishes rendering. Interaction to Next Paint measures the delay between a tap and the screen visibly responding, and replaced First Input Delay in March 2024. Cumulative Layout Shift measures how far content moves while the page settles, which is what makes a reader tap the wrong thing.
How much they matter
Less than the people selling audits imply, and more than developers usually admit. Core Web Vitals are a tiebreaker rather than a lever. They rarely lift a weak page above a strong one, but a slow page loses to an equally relevant fast one, and on mobile a bad LCP loses visitors before ranking is even involved.
The larger effect is commercial rather than algorithmic. A homeowner on a phone in a driveway abandons a page that takes six seconds, whatever position it held in the results.
Lab scores versus real visitors
The score from a testing tool is a simulation run on one synthetic device. The score Google actually uses comes from the Chrome User Experience Report, which is field data collected from real Chrome visitors over a rolling twenty-eight day window. A site can pass in the lab and fail in the field, and only the field number is the one attached to rankings.
| Measurement | Good | Needs work | Poor |
|---|---|---|---|
| Largest Contentful Paint | 2.5s or less | 2.5s to 4.0s | Over 4.0s |
| Interaction to Next Paint | 200ms or less | 200ms to 500ms | Over 500ms |
| Cumulative Layout Shift | 0.1 or less | 0.1 to 0.25 | Over 0.25 |
Where this applies
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