Core Web Vitals

Core Web Vitals are a set of three standardized, field-data-based metrics Google uses to quantify real-world user experience on web pages, forming the basis of Google’s page experience ranking signal. The three current metrics are Largest Contentful Paint (LCP, measuring load speed), Interaction to Next Paint (INP, measuring interactivity), and Cumulative Layout Shift (CLS, measuring visual stability). Google collects these metrics from Chrome users via the Chrome User Experience Report (CrUX) and uses them as a confirmed ranking factor in its algorithm.

How it works

Google measures Core Web Vitals using field data (real user measurements from Chrome browsers) rather than lab simulations. Each metric has defined Good, Needs Improvement, and Poor thresholds: LCP should be under 2.5 seconds, INP under 200 milliseconds, and CLS under 0.1. A page passes Core Web Vitals if at least 75% of real-user sessions meet the Good threshold for all three metrics. Scores are available through Google Search Console, PageSpeed Insights, and the CrUX API.

Key facts

• INP replaced FID: In March 2024, Interaction to Next Paint replaced First Input Delay (FID) as the interactivity metric, measuring the responsiveness of all user interactions rather than just the first.
• Ranking signal scope: Core Web Vitals are a tiebreaker signal, not a dominant ranking factor; highly relevant content can rank well even with poor Core Web Vitals, but they matter at the margin.
• Field vs. lab data: PageSpeed Insights shows both lab data (simulated) and field data (real CrUX); Google’s ranking signal uses field data, which often differs significantly from lab scores.

For builders

For content publishers running WordPress or similar CMS platforms, Core Web Vitals failures are most commonly caused by render-blocking JavaScript, large unoptimized hero images (LCP), ad layout shifts (CLS), and heavy third-party scripts that delay interactivity (INP). Practical improvements include implementing lazy loading for images, using a content delivery network, optimizing the critical rendering path, and deferring non-essential JavaScript. For ad-heavy publishers, controlling CLS from ad slots by reserving space with fixed-height containers before ads load is a particularly impactful fix.

Sources

• Google. Web Vitals documentation. web.dev
• Google. Page experience and Core Web Vitals as ranking signals. developers.google.com
• W3C. Performance Timeline specification. w3.org
• Chromium. Speed and performance metrics documentation. chromium.googlesource.com
• HTTP Archive. Web performance public dataset. httparchive.org