Core Web Vitals: three metrics of usability
Core Web Vitals — three indicators that Google uses to measure page usability for users: the speed of the main content appearing, layout stability, and responsiveness to actions.
Three metrics
| Metric | What it measures | Good value |
|---|---|---|
| LCP | When the main block of the page is visible | Up to 2.5 seconds |
| CLS | How much the layout shifts during loading | Up to 0.1 |
| INP | Delay in response to clicks and input | Up to 200 milliseconds |
Lab and field data
Synthetic runs show how the page behaves under ideal conditions, which is useful for debugging. Field data is collected from real visitors and is what search engines consider. The discrepancy between them is normal: your users have different devices and connections.
What is usually fixed first
- LCP: heavy image of the first screen, slow server response, blocking styles.
- CLS: images without specified sizes, banners and notifications that overlay content.
- INP: heavy scripts and third-party widgets — chats, analytics, pixels.
Where to check your values
Field data is available in the page experience report in Search Console — it groups addresses by problem types, so you can fix entire templates at once, rather than one page at a time. Lab values can be obtained from any synthetic test: they are convenient to take before and after fixes to understand if the change helped.
How much this affects rankings
This is a factor, but not a decisive one: it rather distinguishes pages that are close in other characteristics. It is more useful to consider it as part of conversion work — a slow page loses visitors before they see the offer. You can measure key metrics with speed check, and for the entire site — with audit.