Core Web Vitals are three Google metrics that measure how fast your main content loads (LCP), how quickly your page responds to clicks and taps (INP), and how stable the layout stays while it loads (CLS). To pass, a page needs an LCP of 2.5 seconds or less, an INP of 200 milliseconds or less, and a CLS of 0.1 or less for most real visitors.
In this guide, the technical SEO team at Glorvix.com explains what each metric means, where to check your scores, and which fixes usually make the biggest difference.
Key takeaways
- Core Web Vitals cover loading (LCP), responsiveness (INP) and visual stability (CLS).
- Google’s “good” targets are LCP of 2.5 s or less, INP of 200 ms or less and CLS of 0.1 or less, measured at the 75th percentile of page loads.
- Use Search Console for site-wide field data and PageSpeed Insights to diagnose individual URLs.
- Most wins come from optimising images, cutting heavy JavaScript and reserving space for content that loads late.
What are Core Web Vitals?
Core Web Vitals are a subset of Google’s Web Vitals initiative. They focus on three parts of the user experience that visitors actually feel: waiting for content, waiting for a response, and dealing with content that jumps around.
Google’s documentation says they are used by its ranking systems and recommends that site owners achieve good scores. That said, they are one signal among many. A fast page with weak, irrelevant content will not outrank a genuinely helpful page, so treat them as part of a wider technical SEO programme rather than a magic switch.
The three metrics and their thresholds
The thresholds below come straight from Google’s Web Vitals documentation on web.dev. Google recommends measuring them at the 75th percentile of page loads, split by mobile and desktop.
| Metric | What it measures | “Good” threshold | Common causes of poor scores |
|---|---|---|---|
| Largest Contentful Paint (LCP) | Loading: when the largest visible image or text block renders | 2.5 seconds or less | Slow server response, large hero images, render-blocking CSS and JavaScript |
| Interaction to Next Paint (INP) | Responsiveness: delay between a user interaction and the next visual update | 200 milliseconds or less | Long JavaScript tasks, heavy third-party scripts, large DOM size |
| Cumulative Layout Shift (CLS) | Visual stability: how much visible content shifts unexpectedly | 0.1 or less | Images without dimensions, late-loading ads or embeds, web font swaps |
A page passes the Core Web Vitals assessment only when it meets the “good” target for all three metrics. Note that INP replaced First Input Delay (FID) as the responsiveness metric in 2024, so older guides that mention FID are out of date.
How to measure Core Web Vitals
There are two kinds of data. Field data comes from real Chrome users visiting your site, while lab data comes from a simulated test. Google’s assessment is based on field data, so that is what you should track over time.
Google Search Console
The Core Web Vitals report in Search Console groups your URLs into Good, Needs improvement and Poor, separately for mobile and desktop. It is the best starting point because it shows patterns across templates, such as every blog post or every product page failing the same metric.
Pages need enough real traffic to appear in the report. Smaller sites may see limited data, which is normal.
PageSpeed Insights
PageSpeed Insights shows both field data (when available) and a Lighthouse lab test for a single URL. Use the field section to confirm whether a page passes, and the diagnostics section to find the specific images, scripts or elements causing the problem.
Lab scores can differ from field results because they test one simulated device and connection. Use them to debug, not as your final verdict.
Practical fixes for each metric
At Glorvix.com, we fix issues at the template level wherever possible, because one change to a shared header or product template can improve thousands of URLs at once.
How to improve LCP
- Compress hero images, serve modern formats such as WebP or AVIF, and size them correctly for each screen.
- Do not lazy-load the main above-the-fold image; consider giving it a high fetch priority instead.
- Reduce server response time with good hosting, page caching and a content delivery network.
- Inline critical CSS and defer non-essential CSS and JavaScript so the browser can render content sooner.
How to improve INP
- Break up long JavaScript tasks so the main thread can respond to input between them.
- Audit third-party scripts such as chat widgets, tag managers and trackers, and remove the ones you no longer need.
- Give users immediate visual feedback after a click, then run heavier work afterwards.
- Keep the DOM lean, since very large pages take longer to update after each interaction.
How to improve CLS
- Set width and height attributes (or a CSS aspect ratio) on every image and video.
- Reserve fixed space for ads, embeds and cookie banners before they load.
- Avoid inserting content above existing content unless the user asked for it.
- Preload key web fonts and use sensible fallback fonts to limit text reflow.
Building performance into your site
Many Core Web Vitals problems start at the design stage: oversized sliders, too many plugins and page builders that load scripts on every page. If you are planning a rebuild, it is worth thinking about performance in your web design brief and budget from day one. Our guide to how much web design costs covers the factors that shape that budget.
Redesigns and platform changes are also a common moment for scores to drop. Our SEO website migration checklist includes performance checks to run before and after launch, so regressions are caught early.
Finally, keep monitoring. Field data in Search Console reflects a rolling window of real visits, so improvements take a few weeks to show. Re-check after each major release, theme update or new marketing script.
If you would rather have specialists handle the diagnosis and fixes, the Glorvix.com SEO agency team offers technical SEO services for businesses in the USA and Australia.
Frequently asked questions
Do Core Web Vitals directly affect Google rankings?
Google says Core Web Vitals are used by its ranking systems, but they are only one of many signals. Relevance and content quality matter more. Good scores help most when competing pages are similarly useful, and they also improve the experience for visitors, which can support conversions regardless of rankings.
Why do PageSpeed Insights and Search Console show different results?
PageSpeed Insights runs a lab test on one simulated device, while Search Console reports field data from real Chrome users over a rolling period. Network speed, devices and user behaviour vary, so the numbers often differ. Use field data to judge pass or fail, and lab data to find causes.
How long does it take for Core Web Vitals improvements to show?
Field data is collected over a rolling window of real visits, so fixes usually take several weeks to be fully reflected in Search Console. You can use the validation feature in the report to track progress. Lab tools such as Lighthouse show the effect of a change immediately after deployment.
What replaced First Input Delay?
Interaction to Next Paint (INP) replaced First Input Delay as the Core Web Vitals responsiveness metric in 2024. INP is stricter because it considers interactions throughout the whole visit, not just the first one. A good INP is 200 milliseconds or less at the 75th percentile of page loads.
