Core Web Vitals
A set of three Google-defined metrics, LCP, INP, and CLS, that measure how a page actually performs for real users and contribute to search rankings.
Also known as: CWV, Web Vitals
Core Web Vitals are three Google-defined metrics that measure user-perceived performance of a web page: how quickly it loads, how quickly it responds to interaction, and how stable its layout is during loading. They are a Google search ranking signal and are reported in Google Search Console for sites that meet a minimum traffic threshold.
The three metrics
Largest Contentful Paint (LCP)
The time it takes for the largest visible element in the viewport (typically a hero image or headline block) to render. Google’s published thresholds:
- Good: under 2.5 seconds
- Needs improvement: 2.5–4.0 seconds
- Poor: over 4.0 seconds
LCP approximates how quickly a page appears to load.
Interaction to Next Paint (INP)
The time it takes for the page to visually respond after a user clicks, taps, or types. INP replaced First Input Delay (FID) as the responsiveness metric in March 2024.
- Good: under 200 milliseconds
- Needs improvement: 200–500 ms
- Poor: over 500 ms
Cumulative Layout Shift (CLS)
A measure of how much visible content shifts position unexpectedly during page load. Common causes include images without dimensions, late-loading ads, or web fonts that swap in after the page renders.
- Good: under 0.1
- Needs improvement: 0.1–0.25
- Poor: over 0.25
CLS is a unitless score representing the proportion of the viewport affected by unexpected movement.
Why Core Web Vitals matter
Search rankings. Google uses Core Web Vitals as one of many ranking signals. They function as a tiebreaker among pages with similar relevance and content quality.
Conversion. Multiple studies, including Google’s own and analyses from Amazon, Walmart, and Akamai, have found that slower page performance correlates with lower conversion rates. The magnitude varies by industry and audience.
Field data vs lab data
Google measures Core Web Vitals two ways:
- Field data (real users). Anonymized performance data from Chrome users browsing the site, aggregated in the Chrome User Experience Report (CrUX). Field data is what counts for search rankings.
- Lab data (simulated). Tools like PageSpeed Insights and Lighthouse run a simulated test in a controlled environment. Useful for diagnosis, but not the basis for ranking.
A site can show different scores in lab and field data. The two often diverge because real users have varied devices, networks, and browsing patterns that simulated tests do not fully replicate.
Field data is visible in Google Search Console under the Core Web Vitals report, after roughly 28 days of meaningful traffic.
Common factors that affect scores
Pages that perform poorly on Core Web Vitals typically share one or more characteristics:
- Large JavaScript bundles loaded on every page
- Render-blocking CSS or JavaScript in the document head
- Images served without dimensions, or larger than required
- Late-loading fonts that cause text to shift after rendering
- Third-party scripts (ads, analytics, embeds) that delay interactivity
These factors apply regardless of how the site is built. The architecture of the underlying platform influences how easy or difficult they are to address.
Performance characteristics by site type
| Site type | Typical LCP behavior | Typical CLS behavior | Notes |
|---|---|---|---|
| Hosted CMS platforms (Squarespace, Webflow, Wix) | Often above 2.5s on default templates | Variable, depends on template and embeds | Limited control over what scripts are loaded |
| Self-hosted WordPress | Highly variable | Variable | Depends heavily on theme, plugins, and hosting |
| Static / code-based sites | Often under 2.5s | Often near zero | Smaller payloads and fewer third-party dependencies are common |
Individual results vary; well-optimized sites on any architecture can achieve good scores.
How to check Core Web Vitals
- PageSpeed Insights, paste a URL, see lab and field data
- Chrome DevTools → Lighthouse, built into Chrome
- Google Search Console → Core Web Vitals, real-user data grouped by URL pattern
- Web.dev measure, Google’s diagnostic tool
Common misconceptions
- “A high PageSpeed score means good Core Web Vitals.” PageSpeed reports lab data; rankings use field data. They can disagree.
- “Core Web Vitals only affect ecommerce.” They apply to any page competing in Google search.
- “A plugin can fix Core Web Vitals.” Plugins can address some causes, but underlying architecture often sets a ceiling on what is achievable.