Core Web Vitals are a set of user experience metrics that Google uses as ranking signals. Introduced in 2021 as part of the Page Experience update, they represent Google's attempt to quantify the experience of actually using a webpage — how fast it loads, how stable it is, and how responsive it feels. Poor Core Web Vitals scores can suppress your rankings even if your content, backlinks, and other SEO signals are strong.
The three Core Web Vitals
Largest Contentful Paint (LCP)
LCP measures how long it takes for the largest visible element on the page to load — typically a hero image, large text block, or video. It's a proxy for perceived load speed: the moment the page feels "loaded" to the user.
Target: Under 2.5 seconds. 2.5–4 seconds is "needs improvement." Over 4 seconds is "poor."
Common causes of poor LCP: Large, uncompressed images; render-blocking JavaScript or CSS; slow server response times; no caching.
How to improve: Compress and convert images to WebP format; use a CDN to reduce server response time; implement lazy loading for below-the-fold images; preload the LCP element using ; minimise render-blocking resources.
Cumulative Layout Shift (CLS)
CLS measures visual stability — how much the page layout shifts unexpectedly as it loads. If an image loads in and pushes text down the page, causing you to accidentally click the wrong button, that's a layout shift. It's frustrating for users and measured precisely by CLS.
Target: Under 0.1. 0.1–0.25 is "needs improvement." Over 0.25 is "poor."
Common causes of poor CLS: Images without explicit dimensions; ads or embeds that change size after loading; dynamically injected content above existing content; web fonts that cause FOUT (Flash of Unstyled Text).
How to improve: Set explicit width and height attributes on all images and video elements; reserve space for ads and dynamic content; use font-display: swap for web fonts; avoid inserting content above existing content after page load.
Interaction to Next Paint (INP)
INP (which replaced First Input Delay in 2024) measures the responsiveness of a page to user interactions — how quickly the page responds when you click a button, tap a link, or interact with a form. Poor INP makes a page feel sluggish and unresponsive.
Target: Under 200ms. 200–500ms is "needs improvement." Over 500ms is "poor."
Common causes of poor INP: Long-running JavaScript tasks blocking the main thread; excessive DOM size; unoptimised event handlers; large JavaScript bundles.
How to improve: Break up long JavaScript tasks; defer non-critical JavaScript; optimise event handlers; reduce DOM size where possible; use web workers for complex calculations.
How to measure Core Web Vitals
Google Search Console's Core Web Vitals report shows your field data (real user measurements from the Chrome User Experience Report) for all pages on your site. This is the data Google actually uses for ranking — not lab measurements. PageSpeed Insights provides both lab and field data for individual URLs. Chrome DevTools' Lighthouse tab provides lab measurements for development and debugging.
The ranking impact
Google uses Core Web Vitals as a tiebreaker signal — pages with similar relevance and authority are ranked in favour of those with better Core Web Vitals. For highly competitive queries where many pages are closely matched on content and authority signals, Core Web Vitals can be the deciding factor. For less competitive queries, the impact is smaller but still present. Improving from "poor" to "good" on all three metrics is a worthwhile investment for any site concerned about SEO performance.