If you’ve seen LCP, INP or CLS show up in a Search Console report or a PageSpeed Insights audit and wondered what they actually measure, this is the technical reference. We break down each Core Web Vital, the thresholds Google considers good or poor, and the 2024 update where INP replaced FID.
This page is the metrics deep-dive in our Core Web Vitals cluster. For the SEO and business impact angle, see Core Web Vitals Explained. For how to measure them, see How to measure Core Web Vitals. For practical fixes, see 6 best practices to improve website speed.
Core Web Vitals Explained
Google’s Core Web Vitals (CWV) are a set of three specific performance metrics designed to quantify user experience on a webpage. They focus on loading speed, interactivity, and visual stability. In simple terms, Core Web Vitals measure how fast your content appears, how quickly it responds to input, and how stable it is as it loads. Here are the three Core Web Vitals metrics and what they mean:
- Largest Contentful Paint (LCP) – Loading speed. LCP measures how long it takes to load the largest visible content element on the page (e.g. a hero image or heading). It essentially gauges when the main content is available to the user. A “good” LCP is under 2.5 seconds (for at least 75% of page loads). This is now a common benchmark for acceptable page load time.
- First Input Delay (FID) – Initial interactivity. FID measures the delay between a user’s first interaction (like clicking a button or link) and the browser’s response. It captures that annoying “lag” when you try to click but the page isn’t ready. A good FID was defined as under 100 millisecondsemailvendorselection.com. However, FID has been replaced in 2024 by a more comprehensive metric (see INP below). Google found FID wasn’t telling the whole story of interactivity.
- Interaction to Next Paint (INP) – Overall responsiveness. INP is the new Core Web Vitals (as of March 2024) that replaced FIDweb.dev. Instead of only measuring the first interaction, INP observes all clicks, taps, or key presses during a user’s visit and reports the worst (longest) interaction delay. This provides a better picture of a page’s overall “lagginess” or responsiveness to user actions. A good INP is ≤ 200 ms, and anything above 500 ms is considered poor. blog.cloudflare.comsearchenginejournal.com. In other words, your site should consistently respond to user inputs within a fraction of a second.
- Cumulative Layout Shift (CLS) – Visual stability. CLS measures how much the page’s layout unexpectedly shifts during loading. Have you ever been about to click something, but the page jumps and you click the wrong thing? That’s what CLS captures. It’s measured as a score, not in seconds, and a good CLS score is ≤ 0.1emailvendorselection.com. Low CLS means elements aren’t moving around a lot – a stable, pleasant load experience.
Together, these Core Web Vitals focus on key aspects of UX: does the main content load quickly (LCP)? Is the site responsive when users try to interact (INP)? And does everything stay stable (CLS)? Google uses these metrics as part of its “Page Experience” ranking signals – a fast, responsive, stable site will have an SEO edge over a slow, clunky one. (Google confirmed that Core Web Vitals are a ranking factor in search resultsemailvendorselection.com, though not the only factor – more on that later.)
2024 Update – INP replaces FID: It’s worth noting the recent change: Interaction to Next Paint officially became a Core Web Vital in March 2024, replacing First Input Delayweb.dev. FID is now deprecated because it only measured the first interaction’s delay, whereas INP looks at the full session’s interactivity. This means site owners and developers should focus on INP going forward. If you’ve been tracking FID in tools like Google Lighthouse or Search Console, you’ll have seen INP data appear as the new standard. For agencies, it’s important to educate your team and clients about this change – ensure your audits and reports now highlight INP instead of FID. For SMEs, just know that Google raised the bar: consistently smooth interaction is now being measured, not just the first click. If your site had a decent FID but suffers from slow subsequent interactions (perhaps due to heavy scripts or single-page app behavior), you’ll need to optimise further for INP.
Quick Reference: Good vs Poor Thresholds
- LCP (Largest Contentful Paint) — Good: under 2.5 seconds. Needs improvement: 2.5–4 seconds. Poor: over 4 seconds.
- INP (Interaction to Next Paint) — Good: 200 ms or less. Needs improvement: 200–500 ms. Poor: over 500 ms.
- CLS (Cumulative Layout Shift) — Good: 0.1 or less. Needs improvement: 0.1–0.25. Poor: above 0.25.
Google measures these against the 75th percentile of real user data from the Chrome User Experience Report. Your site needs the majority of page loads to hit the “good” threshold to clear the bar.
Next Steps in the Core Web Vitals Cluster
- Why Core Web Vitals matter for SEO and conversions — the business case and search-ranking impact.
- How to measure Core Web Vitals — PageSpeed Insights, Search Console, Lighthouse, RUM and third-party tools.
- 6 best practices to improve website speed — the tactical fixes that move LCP, INP and CLS.
