Key highlights

  • Core Web Vitals measure loading (LCP), responsiveness (INP), and visual stability (CLS).
  • Google assesses them from real-user field data at the 75th percentile.
  • Good thresholds: LCP ≤ 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1.
  • Fix the biggest bottleneck first — usually the hero image, heavy JavaScript, or unreserved space.

1. What are Core Web Vitals?

Core Web Vitals are three metrics Google uses to describe the real-world experience of a page: how fast the main content loads, how quickly the page responds to interactions, and how stable the layout is while it loads.

They are measured from real visitors (field data, collected in the Chrome User Experience Report) and assessed at the 75th percentile — so a page passes only when at least three out of four visits meet the threshold.

2. Largest Contentful Paint (LCP)

LCP measures how long it takes for the largest image or text block in the viewport to render. On most pages that is a hero image, a banner, or the main heading.

A good LCP is 2.5 seconds or less; anything over 4 seconds is poor.

  • Serve the hero image in a modern format (WebP or AVIF) at the size it is displayed.
  • Never lazy-load the LCP image — load it eagerly and give it high fetch priority.
  • Reduce server response time with caching or a CDN.
  • Remove render-blocking CSS and scripts above the fold.

3. Interaction to Next Paint (INP)

INP measures how quickly the page visually responds after someone clicks, taps, or types. It replaced First Input Delay (FID) as a Core Web Vital in March 2024.

A good INP is 200 milliseconds or less; over 500 milliseconds is poor. Slow INP is almost always caused by too much JavaScript running on the main thread.

  • Break long JavaScript tasks into smaller chunks.
  • Audit third-party scripts (chat widgets, tag managers, ads) and remove what isn't needed.
  • Avoid heavy work in click and input handlers; defer non-urgent updates.

4. Cumulative Layout Shift (CLS)

CLS measures how much visible content unexpectedly moves while the page loads — the moment a button jumps just as you go to tap it.

A good CLS score is 0.1 or less; above 0.25 is poor.

  • Always set width and height (or an aspect ratio) on images and videos.
  • Reserve space for ads, embeds, and banners before they load.
  • Load web fonts so the fallback and final font have similar sizes.

5. How to measure Core Web Vitals

Start with Google Search Console's Core Web Vitals report to see which groups of URLs pass, need improvement, or fail on mobile and desktop.

Then use PageSpeed Insights on a representative URL from each failing group. It shows the field data and a lab test (Lighthouse) with specific diagnostics, so you can see what is slowing the page down.

6. Where to start

Fix the metric that fails for the most important templates first — for example product or service pages — rather than chasing a perfect score on every URL.

After deploying a fix, give the field data time to update: Search Console and the Chrome User Experience Report use a rolling 28-day window, so improvements show up gradually.

Frequently asked questions

Are Core Web Vitals a ranking factor?

They are part of Google's page experience signals, but relevance and content quality matter far more. Good Core Web Vitals help most when competing pages are otherwise similar.

Why do PageSpeed Insights and Search Console show different results?

PageSpeed Insights shows lab data from a single simulated load alongside field data, while Search Console groups real-user field data across many URLs over a 28-day window.

What replaced First Input Delay (FID)?

Interaction to Next Paint (INP) replaced FID as a Core Web Vital in March 2024. INP looks at the responsiveness of interactions across the whole visit, not just the first one.