What is Core Web Vitals?

Core Web Vitals are three Google-defined metrics that measure real-world page experience: Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP).

Largest Contentful Paint measures how long the largest visible element on your screen takes to load. This might be a hero image or a large block of text. To provide a good user experience, Google suggests a target of under 2.5 seconds. Cumulative Layout Shift calculates how much the content of a page moves around unexpectedly during the loading process. A score below 0.1 is required to ensure that users do not accidentally click the wrong button when a page jumps. Interaction to Next Paint tracks how quickly the page responds to a physical user interaction, such as clicking a link or a menu. The target for this metric is under 200 milliseconds. This recently replaced First Input Delay (FID) as it provides a more comprehensive view of responsiveness throughout the entire page lifecycle.

Google has used these metrics as an official ranking signal since 2021. They are weighted alongside traditional signals like content quality and brand reputation. While they are not usually the most dominant factor, they serve as a critical tiebreaker between otherwise similar pages. If two sites have equally good content, the one with superior Core Web Vitals will almost certainly rank higher. This is Google's way of forcing site owners to prioritise the actual human experience of the web over technical shortcuts that only benefit robots.

Common causes of failure are often technical in nature. Render-blocking JavaScript and unoptimised large images frequently slow down the loading process. For LCP, ensuring that your main image or text block is preloaded and not "lazy-loaded" is a common fix. For CLS, defining explicit width and height attributes in your CSS for all media elements prevents the browser from guessing their size and causing jumps. Low-quality hosting or slow server response times (TTFB) can also drag down all three scores simultaneously.

Measuring these vitals is possible through several official tools. Google PageSpeed Insights provides a lab-based view of your performance. The Core Web Vitals report in Search Console shows real-world data from actual users over a 28-day rolling period. You can also monitor the Chrome User Experience Report (CrUX) for historical trends. For a deeper dive into remediation strategies and how these metrics impact your commercial conversion rates, see our guide on core web vitals explained. Ensuring your site is "passing" these tests is the baseline for competitive performance in 2026.