Core Web Vitals: LCP, INP and CLS Explained
Short answer: Core Web Vitals are three measurements Google uses to judge how a page feels to real visitors. LCP (Largest Contentful Paint) is how fast the main content shows up; aim for 2.5 seconds or less. INP (Interaction to Next Paint) is how fast the page reacts to clicks and taps; aim for under 200 milliseconds. CLS (Cumulative Layout Shift) is how much the layout jumps around; aim for 0.1 or less. A page passes when at least 75% of real visits meet all three.
The thresholds
| Metric | Measures | Good | Poor |
|---|---|---|---|
| LCP | Loading: when the largest image or text block appears | ≤ 2.5 s | > 4.0 s |
| INP | Responsiveness: delay from a click, tap or key press to the next screen update | < 200 ms | > 500 ms |
| CLS | Visual stability: how much visible content moves unexpectedly | ≤ 0.1 | > 0.25 |
Values in between are “needs improvement”. Google judges each at the 75th percentile of page visits, split into mobile and desktop. So a page passes when three out of four visits are in the good range. INP replaced First Input Delay (FID) as a Core Web Vital in March 2024.
Do Core Web Vitals affect rankings?
Yes, but don’t overrate them. Google’s documentation says good Core Web Vitals, along with other page experience aspects, align with what its core ranking systems “seek to reward”, and it recommends achieving them “for success with Search.” Its page experience guide adds that good scores don’t guarantee top rankings, and that Google “always seeks to show the most relevant content, even if the page experience is sub-par.” So a fast page with weak content won’t outrank a slower page that answers the query better. Fix them for your visitors first; any ranking benefit comes on top.
Field data vs lab data
This is where most confusion comes from:
- Field data comes from real Chrome users (the Chrome User Experience Report). It’s what Google uses for the pass/fail assessment. You see it in Search Console’s Core Web Vitals report and at the top of PageSpeed Insights.
- Lab data is one simulated load (Lighthouse, Chrome DevTools, the lower part of PageSpeed Insights, WebPageTest). It helps you debug, but it isn’t your score. Lab tests can’t measure INP, because no one clicks; they use Total Blocking Time as a stand-in.
Small sites often have no field data at all, because not enough Chrome users visit. Then Search Console shows nothing and PageSpeed Insights shows only lab results.
Where to check yours
- Search Console → Experience → Core Web Vitals: groups of similar URLs marked Good, Needs improvement or Poor, for mobile and desktop.
- PageSpeed Insights (pagespeed.web.dev): field data for one URL or the whole origin, plus a lab run with suggestions.
- Chrome DevTools → Performance: live LCP, INP and CLS while you use the page, and the elements behind each.
How to fix each metric
LCP: make the main content arrive sooner
web.dev splits LCP into four parts: server response (TTFB), the delay before the main image starts loading, the time it takes to load, and the delay before it is drawn. The biggest wins are usually a faster server response, making the main image discoverable in the HTML with fetchpriority="high", and never lazy-loading it. Full guide: how to fix Largest Contentful Paint.
INP: keep the main thread free
Slow interactions come from long JavaScript tasks running when the user clicks. Break up long tasks, cut unused scripts (third-party tags often), and do less work in click handlers. Guide: INP optimization.
CLS: reserve space before content loads
Give images and videos width and height, reserve space for ads and embeds, don’t insert content above what’s already visible, and handle web fonts so text doesn’t reflow. Guide: how to fix Cumulative Layout Shift.
A practical order of work
- Open the Core Web Vitals report and start with the URL group that has the most “Poor” mobile URLs.
- Run one example URL in PageSpeed Insights and note which metric fails in the field.
- Find the cause in DevTools (the LCP element, the shifting element, or the slow interaction).
- Fix it in the template, not the single page, since one template usually serves the whole group.
- Click Validate fix. Field data covers the previous 28 days, so improvements show up gradually.
One check you can run with our free sitemap checker: it flags sitemap URLs that take more than 3 seconds to respond, a sign of a slow server (TTFB) that drags LCP down. It doesn’t measure Core Web Vitals themselves; use PageSpeed Insights for that. See also TTFB optimization.
Frequently asked questions
What are the three Core Web Vitals?
Largest Contentful Paint (LCP) for loading, Interaction to Next Paint (INP) for responsiveness, and Cumulative Layout Shift (CLS) for visual stability.
What scores do I need to pass?
LCP of 2.5 seconds or less, INP under 200 milliseconds, and CLS of 0.1 or less, measured at the 75th percentile of real visits, separately for mobile and desktop.
Are Core Web Vitals a ranking factor?
They count, but modestly. Google says good Core Web Vitals align with what its core ranking systems seek to reward, but also that they don’t guarantee top rankings and that it shows the most relevant content even when page experience is sub-par.
Why does PageSpeed Insights show different numbers from Search Console?
PageSpeed Insights shows a lab test (one simulated load) and field data from real Chrome users. Search Console uses field data only, grouped across similar URLs. Pass or fail is judged on field data.
What happened to FID?
First Input Delay was replaced by Interaction to Next Paint as a Core Web Vital in March 2024. INP measures the delay across all interactions on the page, not just the first.