Core Web Vitals, explained without the jargon

Core Web Vitals are three measurements Google uses to judge how a page feels to use: how fast the main content appears (LCP), how quickly the page responds to a tap or click (INP), and how much the layout jumps while it loads (CLS). A page passes when at least 75% of real visits meet the “good” threshold for all three.

The three numbers, and what counts as good

• Largest Contentful Paint (LCP): the main image or heading appears within 2.5 seconds
• Interaction to Next Paint (INP): the page responds to input within 200 milliseconds
• Cumulative Layout Shift (CLS): a layout shift score of 0.1 or less

INP replaced the older First Input Delay metric in March 2024. It is stricter, because it looks at every interaction on the page, not only the first one.

Lab data versus field data

Lighthouse runs a test on one simulated device and is useful for finding problems. Google’s ranking signal uses field data: what real visitors experienced over the last 28 days, reported in Search Console and PageSpeed Insights. A page can score well in Lighthouse and still fail in the field if most visitors use slower phones.

Fixes that move LCP

• Serve the main image in a modern format, at the size it is displayed
• Preload the main image and the fonts used above the fold
• Avoid hiding the main content behind sliders or JavaScript
• Reduce server response time with caching and better hosting

Fixes that move INP

• Remove or delay third-party scripts that are not essential
• Split long JavaScript tasks so the browser can respond in between
• Load chat widgets and trackers after the page is interactive

Fixes that move CLS

• Give every image and video a width and height
• Reserve space for embeds and banners before they load
• Use font fallbacks that match the size of your web font

Do Core Web Vitals affect rankings?

Yes, as one of Google’s page experience signals, but relevant content matters more. The stronger reason to fix them is visitors: people leave slow, jumpy pages before they read a word. We measure every key page before and after our changes, so you can see what moved.

Written byMuhammad AhmadFounder & Software Engineer at StackStead Solutions. Building for the web since 2020.Ask a question