Core Web Vitals explained: LCP, INP and CLS thresholds
Core Web Vitals are the three page-experience measurements Google publishes targets for. This guide gives each metric, what it measures, the exact thresholds from web.dev, how CLS is calculated and the common causes of failure. It belongs to websites, SEO and AdSense; the related sitemap guide is XML sitemaps, and the readiness checks for ad programs are in the AdSense approval checker.
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The three metrics and their thresholds
| Metric | Measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| Largest Contentful Paint (LCP) | Loading: render time of the largest image, text block or video visible in the viewport, relative to when the user first navigated to the page | 2.5 s or less | 2.5 to 4.0 s | More than 4.0 s |
| Interaction to Next Paint (INP) | Responsiveness: time from an interaction until the browser paints the next frame, across all clicks, taps and key presses | 200 ms or less | 200 to 500 ms | More than 500 ms |
| Cumulative Layout Shift (CLS) | Visual stability: the largest burst of unexpected layout shifts during the page's lifetime | 0.1 or less | 0.1 to 0.25 | More than 0.25 |
web.dev says to assess each metric at the 75th percentile of page loads, segmented by mobile and desktop, and that a page passes when it meets the targets for all three. The "needs improvement" range for LCP and CLS is the span between the good and poor thresholds shown on web.dev's pages.
LCP: what counts
LCP candidates are image elements (the first frame time for animated images), images inside SVG, video elements (the poster image or first frame, whichever is earlier), elements with a CSS background image loaded through url() (but not gradients), and block-level elements that contain text. LCP also includes unload time from the previous page, connection setup, redirects and other server delay.
INP: what counts
INP covers mouse clicks, touchscreen taps and key presses. Scrolling, hovering and zooming are not observed. For most sites the worst interaction is reported; on pages with many interactions, web.dev says one highest interaction is ignored for every 50. INP replaced First Input Delay as a stable Core Web Vital in 2024.
CLS: how it is scored
Layout shift score = impact fraction x distance fraction. The impact fraction is the combined visible area of unstable elements across the previous and current frames as a fraction of the viewport; the distance fraction is the greatest distance an unstable element moved divided by the viewport's largest dimension. With an impact fraction of 0.75 and a distance fraction of 0.25 the score is 0.1875, well above the 0.1 target. Shifts that happen less than a second apart are grouped into windows of at most five seconds, and CLS is the highest cumulative window score.
Common causes of a poor score
- CLS: images or videos without width and height, font swaps that change text size, third-party ads or widgets that resize after loading, resources that load late, and content injected above what the visitor is reading.
- LCP: a slow server response, redirects and a large hero image or text block that renders late.
- INP: work that keeps the browser from painting after a click or tap. Measure real interactions to find which ones are slow.
web.dev's pages describe how to measure these metrics in the field and in the lab; use real-user data where you can, since the thresholds apply to the 75th percentile of actual page loads.
Frequently asked questions
What are the Core Web Vitals?
Three metrics Google uses to describe page experience: Largest Contentful Paint (loading), Interaction to Next Paint (interactivity) and Cumulative Layout Shift (visual stability).
What counts as good?
LCP within 2.5 seconds, INP of 200 milliseconds or less, and CLS of 0.1 or less, measured at the 75th percentile of page loads and segmented by mobile and desktop.
What replaced First Input Delay?
Interaction to Next Paint. It became a stable Core Web Vital in 2024. FID measured only the input delay of the first interaction, while INP observes all clicks, taps and key presses on the page.
How is CLS calculated?
Layout shift score = impact fraction x distance fraction. Shifts are grouped into session windows (less than 1 second apart, at most 5 seconds long) and CLS is the highest cumulative score among them. web.dev's example: 0.75 x 0.25 = 0.1875.
What commonly causes layout shift?
Images or videos without known dimensions, fonts that render differently from their fallbacks, third-party ads or widgets that resize after loading, asynchronously loaded resources, and DOM elements added above existing content.
Sources
- web.dev: Web Vitals
- web.dev: Largest Contentful Paint (LCP)
- web.dev: Interaction to Next Paint (INP)
- web.dev: Cumulative Layout Shift (CLS)
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