What are Core Web Vitals? They are a set of metrics Google uses to measure how fast, stable and responsive a page feels to real users. Unlike lab-only tests, they reflect actual visitor experience and act as ranking signals. There are three core metrics: LCP, CLS and INP.
LCP: Largest Contentful Paint
LCP measures when the largest visible content element, usually a big image or block of text, finishes loading. It represents the moment the page feels loaded. A good LCP is under 2.5 seconds.
- —Reduce server response time with quality hosting.
- —Optimize and prioritize large above-the-fold images.
- —Reduce render-blocking CSS and JavaScript.
CLS: Cumulative Layout Shift
CLS measures unexpected movement of content while the page loads. Clicking the wrong button because a late image pushed the layout is the classic example. A good CLS is under 0.1.
- —Set explicit width and height for images and videos.
- —Reserve fixed space for ads and embeds.
- —Load fonts without causing text to shift.
INP: Interaction to Next Paint
INP measures how long the page takes to respond visually after a click, tap or key press. It reflects how responsive the site feels. A good INP is under 200 milliseconds.
- —Break heavy JavaScript tasks into smaller pieces.
- —Remove unused scripts.
- —Keep third-party code from blocking the main thread.
How to Measure
Core Web Vitals are evaluated with two types of data: real-user data (field data) and lab data. Google's free tools show both. Field data aggregates the experience of real visitors to your site, while lab data lets you test in a controlled environment. For lasting improvement, track field data — that is what affects rankings.
Why It Matters
Core Web Vitals are not just technical numbers; they map directly to user satisfaction. A site that loads fast, stays stable and responds instantly keeps visitors and improves conversions, aligning performance and SEO under one roof.