What Are Core Web Vitals? LCP, INP & CLS Explained
Abbreviation: CWV
Core Web Vitals are three specific, standardised metrics — Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) — that Google uses to measure real-world user experience on a page.
Last reviewed: 3 August 2026 · Reviewed by iNet Ventures Technical SEO Team
In plain English
Rather than measuring page speed with one vague number, Google settled on three specific, measurable aspects of user experience: how fast the main content appears (LCP), how quickly the page responds when someone interacts with it (INP), and how much the layout unexpectedly jumps around while loading (CLS). Each has an official "good," "needs improvement," and "poor" threshold, based on real visitor data rather than a lab simulation.
Technical definition
Core Web Vitals are field metrics defined and measured by Google via the Chrome User Experience Report (CrUX), which aggregates anonymised, real-world performance data from Chrome users. Each metric's classification is based on the 75th percentile of page loads across all visitors, segmented by mobile and desktop. A page is classified as "good" for a metric only if at least 75% of visits meet the "good" threshold for that metric. Interaction to Next Paint replaced First Input Delay (FID) as the third official Core Web Vital in March 2024, because FID only measured the delay before the first interaction started, while INP measures responsiveness across every interaction throughout the full page visit.
Quick example
A page with a 75th-percentile LCP of 2.1 seconds, INP of 150ms, and CLS of 0.05 across real visitor data would pass all three Core Web Vitals thresholds as "good" — the kind of profile Google's PageSpeed Insights and Search Console report as a clean pass.
Quick facts
| Meaning | Google's three official field metrics for loading, interactivity, and visual stability |
|---|---|
| Main category | Technical SEO |
| Used by | Developers and SEOs optimising page experience; measured in PageSpeed Insights and Search Console |
| Difficulty | Intermediate |
| Importance | High |
| Common examples | Slow hero images (poor LCP), heavy JavaScript blocking clicks (poor INP), ads or fonts loading late and shifting content (poor CLS) |
| Still relevant? | Yes — actively maintained by Google, with INP replacing FID as the interactivity metric in March 2024. Google has said the metrics themselves are expected to remain stable with an annual review cadence. |
Why Core Web Vitals matters
Core Web Vitals sit at the intersection of genuine user experience and a confirmed (if modest) Google ranking signal.
They are part of Google's Page Experience signals
Core Web Vitals form part of the page experience ranking signals Google uses, though Google has consistently said great content that doesn't meet the thresholds can still outrank content that does — they are one input among many, not a gatekeeper.
They are measured from real visitors, not lab tests
Because Core Web Vitals use CrUX field data, they reflect what actual visitors on real devices and networks experienced — which can differ meaningfully from a clean lab test run on a fast connection.
INP replaced FID for a good reason
FID only measured the delay before a single first interaction. INP assesses responsiveness across every interaction during a visit, giving a far more complete picture of whether a page actually feels responsive to use.
Poor Core Web Vitals often signal deeper UX problems
A poor CLS score usually means real users are experiencing accidental clicks and jarring layout jumps; a poor LCP usually means real users are waiting and leaving. Fixing the metric fixes the underlying experience, not just a number.
How it works
The three metrics and their official "good" thresholds, measured at the 75th percentile.
- 1
Largest Contentful Paint (LCP) — loading
Measures when the largest visible content element (usually a hero image or heading) finishes rendering. Good: 2.5 seconds or less.
- 2
Interaction to Next Paint (INP) — interactivity
Measures how long the page takes to visually respond after a user interaction, across all interactions during the visit. Good: 200 milliseconds or less.
- 3
Cumulative Layout Shift (CLS) — visual stability
Measures the total unexpected movement of visible content during the page's lifespan, scored as a unitless number. Good: 0.1 or less.
- 4
The 75th percentile rule
A page or site passes a given metric only if at least 75% of real visits meet the "good" threshold — a handful of fast connections passing doesn't offset a slow experience for most visitors.
Best practices
Target the 75th percentile across mobile and desktop separately, since experiences differ substantially.
What to do
- Optimise and preload the LCP element (typically a hero image) and avoid render-blocking resources above the fold
- Break up long JavaScript tasks and minimise main-thread work to improve INP
- Reserve explicit width and height (or aspect-ratio) for images, embeds, and ads to prevent CLS
- Monitor field data in Search Console's Core Web Vitals report, not just lab scores from a single test run
- Segment results by mobile and desktop, since thresholds and real performance often differ significantly between them
What to avoid
- Optimising only for a lab tool score (e.g. Lighthouse) while ignoring real-world CrUX field data
- Loading ads, fonts, or embeds without reserved space, causing late layout shifts
- Treating Core Web Vitals as a hard ranking gate — strong, relevant content can still outrank a technically faster page
- Ignoring INP because FID used to be easier to pass — INP is a stricter, more representative measure of real responsiveness
Common mistakes
Confusing lab data with field data
A single Lighthouse run in a controlled environment is a lab test. Core Web Vitals for ranking purposes are based on real, aggregated CrUX field data from actual visitors, which can look very different.
Assuming Core Web Vitals alone determine rankings
Google has repeatedly said page experience signals, including Core Web Vitals, are a modest factor. Highly relevant, high-quality content can and does outrank technically faster pages with weaker content.
Not accounting for the 75th-percentile methodology
A page can look fine on average while still failing the "good" threshold, because the classification depends on the 75th-percentile value, not the mean.
Core Web Vitals as UX metrics first, ranking factor second
It's easy to treat Core Web Vitals purely as an SEO checkbox, but they were designed by Google's web performance team as genuine, research-backed measures of user experience — the ranking application came second. The INP threshold in particular reflects real research into perceptible response-time delays, not an arbitrary number. Sites that treat Core Web Vitals work as a genuine performance investment, rather than a one-off audit to satisfy a tool, tend to see the more durable benefits: lower bounce rates and better engagement, with any ranking benefit as a secondary effect.
- The three metrics and their thresholds are grounded in UX research, not chosen arbitrarily
- Field data (CrUX) is what counts for classification, not isolated lab test runs
- INP is a meaningfully stricter, more complete interactivity metric than the FID it replaced
- Core Web Vitals are one of many page experience signals, not a dominant ranking factor on their own
How iNet Ventures approaches core web vitals
For clients building content and earning links at scale, we flag Core Web Vitals issues that could undermine the value of the content and outreach work itself.
Baseline check before major content pushes
Before large content or digital PR campaigns, we check that the target pages meet reasonable Core Web Vitals thresholds, since a slow page undermines the value of the traffic and links a campaign earns.
Continue learning
Frequently asked questions
What replaced First Input Delay (FID)?
Interaction to Next Paint (INP) officially replaced FID as the third Core Web Vital in March 2024. INP measures responsiveness across all interactions during a page visit, rather than just the delay before the first one.
What are the official "good" thresholds for Core Web Vitals?
LCP: 2.5 seconds or less. INP: 200 milliseconds or less. CLS: 0.1 or less. Each is measured at the 75th percentile of real visits, segmented by mobile and desktop.
Do Core Web Vitals directly affect Google rankings?
They are part of Google's page experience signals, but Google has said they are a modest ranking factor. Strong, relevant content can outrank a page with better Core Web Vitals scores but weaker content.
Where can I check my site's real Core Web Vitals data?
Google Search Console's Core Web Vitals report and PageSpeed Insights both show CrUX field data, which reflects real visitor experience rather than a single lab test.
Written directly from Google's web.dev Core Web Vitals documentation and official threshold definitions, including the March 2024 INP transition.
- Written by:
- iNet Ventures Editorial Team
- Reviewed by:
- iNet Ventures Technical SEO Team
- Published:
- 3 August 2026
- Last reviewed:
- 3 August 2026
Sources and further reading
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