The essentials
- Definition: the Core Web Vitals are three metrics defined by Google to measure a page's loading, responsiveness and visual stability.
- "Good" thresholds: LCP at or below 2.5s, INP at or below 200ms, CLS at or below 0.1, measured at the 75th percentile of real visits.
- Data source: the Chrome User Experience Report (CrUX) — real Chrome visitors, not a laboratory test.
- SEO weight: a light tie-breaker; it never makes up for weak content, but a site marked "needs improvement" loses out on contested queries.
The Core Web Vitals are a set of three metrics defined by Google to quantify a web page's user experience: how fast the main content appears, how responsive it is to interaction, and how visually stable it is. Introduced in 2020 and built into ranking in 2021, they form the measurable part of the "page experience" signal. This article defines each metric and how it is measured; the technical fixes are covered in the Core Web Vitals guide.
The three metrics and their thresholds
| Metric | What it measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Time until the largest visible element appears (an image, a heading, a block of text) | ≤ 2.5s | 2.5 to 4s | > 4s |
| INP (Interaction to Next Paint) | The delay between an interaction (click, tap, key) and the next visual update, across the whole visit | ≤ 200ms | 200 to 500ms | > 500ms |
| CLS (Cumulative Layout Shift) | The sum of unexpected element movements over the page's lifetime | ≤ 0,1 | 0.1 to 0.25 | > 0,25 |
INP replaced FID (First Input Delay) on 12 March 2024. The difference matters: FID only measured the delay of the first interaction, whereas INP takes the worst interaction representative of the whole visit — which pushed many sites from green to amber.
How Google measures: field versus lab
Ranking relies exclusively on field data : measurements collected from real Chrome users who have agreed to share statistics, aggregated in the Chrome User Experience Report (CrUX) over a rolling 28 days. The value used is the 75th percentile : a page is "good" if 75% of its visits meet the threshold. Laboratory tools (Lighthouse, and the diagnostic part of PageSpeed Insights) simulate a visit under fixed conditions; they are for identifying causes, not for judging status.
| Tool | Type of data | Use |
|---|---|---|
| Search Console, Core Web Vitals report | Field (CrUX), by URL group | Knowing which pages need fixing, mobile and desktop separately |
| PageSpeed Insights | Field (at the top) and lab (below) | Diagnosing a specific URL |
| Lighthouse (Chrome DevTools) | Lab | Reproducing and testing a fix |
| The Web Vitals extension, the web-vitals.js library | Field, on your own visitors | Continuous measurement, sent to GA4 or a tracking tool |
A page with too few visits has no CrUX data: Search Console doesn't show it, and Google falls back on the similar URL group or on the domain. Classic speed testing tools do not replace that field measurement.
What weight they carry in search
Google has always described the Core Web Vitals as one signal among hundreds, which "does not replace relevant content". The observations agree: moving from "poor" to "good" doesn't lift a page on its own, but a site entirely "poor" on mobile is at a disadvantage on competitive queries, and the indirect gains are real: fewer abandonments, better conversion rate, crawl budget better used. In 2026 the metric causing small business sites the most trouble is INP, degraded by third-party scripts (consent banners, chat widgets, an overloaded tag manager).
The most frequent causes
- LCP: an unoptimised main image or one loaded lazily, a slow server (TTFB above 800ms), render-blocking CSS, web fonts arriving late.
- INP: third-party JavaScript running on click, long tasks on the main thread, heavy framework hydration.
- CLS: images and iframes without dimensions, banners inserted after load, fonts that change size, adverts.
These metrics belong to the technical section of an SEO audit, alongside response codes and indexing.
How GreenRed helps
Rather than juggling several tools, GreenRed's Site health module brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
What are the three Core Web Vitals in 2026?
LCP (Largest Contentful Paint) for how fast the main content appears, threshold 2.5 seconds; INP (Interaction to Next Paint) for responsiveness, threshold 200 milliseconds; CLS (Cumulative Layout Shift) for visual stability, threshold 0.1. INP replaced FID in March 2024.
Are the Core Web Vitals a ranking factor?
Yes, since 2021, but with limited weight. They are part of the page experience signal and mostly serve to separate content of comparable relevance. An excellent score doesn't make up for weak content; a poor status penalises you mainly on mobile and on contested queries.
Why do PageSpeed Insights and Search Console give different results?
PageSpeed Insights shows both field data (CrUX) and a laboratory test simulating a visit under fixed conditions. Search Console shows only field data, aggregated over 28 days and by page group. Only field data counts for ranking.
Is a site with no CrUX data penalised?
No. If a page or a site gets too few visits to produce field data, Google can't apply the signal and assigns neither bonus nor penalty. Search Console then shows no data for those URLs, which is not a problem in itself.