What are Core Web Vitals?
Core Web Vitals are Google’s three user-experience metrics: Largest Contentful Paint (loading, good at 2.5 seconds or less), Interaction to Next Paint (responsiveness, good at 200 milliseconds or less) and Cumulative Layout Shift (visual stability, good at 0.1 or less). Google assesses them at the 75th percentile of real visits.
The three metrics at a glance
| Metric | Measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | How quickly the main content appears | 2.5 s or less | 2.5 to 4 s | More than 4 s |
| INP (Interaction to Next Paint) | How quickly the page responds to taps and clicks | 200 ms or less | 200 to 500 ms | More than 500 ms |
| CLS (Cumulative Layout Shift) | How stable the layout stays while loading | 0.1 or less | 0.1 to 0.25 | More than 0.25 |
How Google measures them
Google uses field data from real Chrome users, collected in the Chrome UX Report. A page passes a metric when at least 75 percent of visits meet the “good” threshold. Lab tools such as Lighthouse are useful for diagnosing problems, but the numbers that count are the real-user ones. INP replaced First Input Delay as a Core Web Vital in March 2024.
How to improve LCP
- Optimize the hero image: correct dimensions, modern formats such as WebP or AVIF, and load it with high priority.
- Reduce server response time with caching, a CDN and server-side or static rendering.
- Remove or defer render-blocking CSS and JavaScript.
- Preload critical assets such as the main font and hero image.
- Avoid loading the largest element with client-side JavaScript.
How to improve INP
- Break up long JavaScript tasks so the browser can respond between them.
- Ship less JavaScript and avoid heavy hydration on pages that do not need it.
- Defer or remove third-party scripts that block the main thread.
- Keep event handlers light and move heavy work to web workers.
- Give instant visual feedback on taps, then do the work.
How to improve CLS
- Set width and height, or an aspect ratio, on images, video and embeds.
- Reserve space for ads, banners and late-loading components.
- Never insert new content above content the user is already reading.
- Load fonts with a sensible fallback so text does not jump.
- Animate with transforms and opacity instead of properties that move layout.
How to measure
- Google Search Console: the Core Web Vitals report shows field data for your pages.
- PageSpeed Insights: combines real-user data with a lab test.
- Chrome DevTools and Lighthouse: diagnose causes in your own browser.
- The web-vitals JavaScript library: collect the metrics from your own visitors.
Do Core Web Vitals affect rankings?
They are part of Google’s page experience signals, so they can help, but relevance and content quality matter far more. The larger benefit is commercial: faster, steadier pages keep visitors and convert more of them.
Key takeaway: Fix the slowest, highest-traffic templates first. One improved template can move many URLs at once.
Frequently asked questions
What replaced First Input Delay?
Interaction to Next Paint (INP) replaced First Input Delay as a Core Web Vital in March 2024. INP looks at the responsiveness of all interactions during a visit, not just the first.
Is a good Lighthouse score enough?
No. Lighthouse is a lab test on one device and connection. Google judges real-user field data, so check Search Console and PageSpeed Insights as well.
How long until improvements show in Search Console?
Field data is collected over a rolling 28-day window, so improvements appear gradually as new visits replace old ones.
Do Core Web Vitals matter for small sites?
Yes. Speed and stability help every site’s users and conversions, even where traffic is too low to appear in field reports.