SEO

Core Web Vitals

Also known as: CWV, Web Vitals, Core Web Vitals 2024

Core Web Vitals (CWV) are a set of three performance metrics defined by Google that quantify the perceived user experience of a web page: LCP (Largest Contentful Paint), INP (Interaction to Next Paint, replacing FID since 03/2024) and CLS (Cumulative Layout Shift). They have been a direct ranking factor since the Page Experience Update in 2021 and are collected via the Chrome User Experience Report (CrUX) on the basis of real user data.

The three metrics in detail

LCP (Largest Contentful Paint) — measures how long it takes for the largest visible element (usually the hero image or H1) to be rendered. Good: < 2.5 s. Needs improvement: 2.5–4 s. Poor: > 4 s.
INP (Interaction to Next Paint) — measures the response time to all clicks/taps/key presses in a session and takes the worst percentile. Has replaced FID since March 2024. Good: < 200 ms. Poor: > 500 ms.
CLS (Cumulative Layout Shift) — measures visual stability: how much layout elements still jump around during loading. Good: < 0.1. Poor: > 0.25.

Why Core Web Vitals matter for SEO

Google uses CWV as a direct ranking factor — with otherwise equal content, the faster page wins. In addition, conversion rates fall measurably with every second of loading time, which indirectly also worsens engagement signals (time on page, bounce). On mobile, Google weights the CWV more heavily than on desktop (mobile-first indexing).

How to measure Core Web Vitals

Three levels: (1) Lab data from Lighthouse or PageSpeed Insights (synthetic, a single test run). (2) Field data from CrUX (real users, 28-day median). (3) Real User Monitoring (RUM) via your own tracking scripts (Sentry, web-vitals.js). Only the 75th percentile of the field data counts for rankings.

Example from practice

Example: A product page has an LCP of 3.8 s (amber), an INP of 240 ms (amber) and a CLS of 0.18 (amber). With image optimisation (LCP → 1.9 s) and reserving slots for dynamically loaded banners (CLS → 0.05), two of the three metrics improve to ”good”, which typically shows measurable ranking effects in the visibility trend after 4–8 weeks.

Frequently asked questions

How important are Core Web Vitals as a ranking factor?

Core Web Vitals have been a direct ranking factor since the Page Experience Update in 2021, but are weighted moderately: with otherwise equal content, the faster page wins, yet outstanding content beats mediocre CWV. On mobile, Google weights the metrics more heavily than on desktop (mobile-first indexing). Practical rule of thumb: those who move from the red into the amber range usually see ranking effects; going from amber to green tends to matter only for highly competitive keywords.

What is the difference between lab and field data for Core Web Vitals?

Lab data (Lighthouse, PageSpeed Insights) comes from a single synthetic test run and is reproducible, but not representative. Field data (CrUX) is based on real Chrome users over 28 days and uses the 75th percentile. Only the 75th percentile of the field data counts for rankings — lab values are merely a diagnostic tool. That explains why a page with a poor lab LCP can still have green CrUX values (the lab bot waits for everything, real users see the LCP earlier).

Why has INP replaced FID since 2024?

First Input Delay (FID) only measured the very first interaction of a session and was usually very low — even on pages with poor responsiveness. Interaction to Next Paint (INP) measures all clicks, taps and key presses and takes the worst percentile. This reflects the actual user experience far better. Many pages that were green under FID fall back to amber or red under INP — above all JavaScript-heavy SPAs with long task queues.

Which tools measure Core Web Vitals reliably?

For field data: Google Search Console (Core Web Vitals report), the CrUX dashboard, PageSpeed Insights (which shows both). For lab data: Lighthouse (locally in Chrome DevTools), PageSpeed Insights and WebPageTest. For continuous monitoring, SaaS tools with RUM (Real User Monitoring) such as Sentry, SpeedCurve or your own implementations with web-vitals.js are suitable. Rankmio integrates PageSpeed Insights field data directly into the site audit and shows the 28-day trend per page.

Used in Rankmio for

PageSpeed + Core Web Vitals in the site audit

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Last updated: 2026-06-29 · Browse all glossary entries