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Core Web Vitals are Google’s three metrics for measuring real-world page experience: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). They are measured from real user data, not lab tests, and a URL must meet all three thresholds to pass.

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The three metrics

Thresholds are assessed at the 75th percentile of page loads, segmented by mobile and desktop. Passing means 75% of real visits met the threshold — not the average. INP replaced First Input Delay as a Core Web Vital in March 2024. FID measured only the delay before the first interaction was processed; INP measures the full interaction-to-paint latency across all interactions on the page.

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Common causes on ecommerce sites

LCP — unoptimised hero and product imagery, render-blocking CSS or fonts, slow server response, oversized image dimensions served to mobile. INP — heavy third-party scripts (chat widgets, analytics, review platforms, A/B testing tools), long JavaScript tasks blocking the main thread, unoptimised event handlers on filters and variant pickers. CLS — images and embeds without explicit dimensions, banners and cookie notices injected above existing content, web fonts causing layout reflow, dynamically inserted promotional bars.

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How they are measured

  • Field data — the Chrome User Experience Report (CrUX), based on real Chrome visits over a rolling 28-day window. This is what Google uses for assessment.
  • Lab data — Lighthouse and PageSpeed Insights simulations. Useful for diagnosis, but does not directly determine the assessment.
Because field data uses a 28-day rolling window, fixes take weeks to show up fully.

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Weight in ranking

Core Web Vitals are a genuine but small ranking signal. Relevance and content quality dominate. They matter most as a tiebreaker between comparably relevant pages — and independently for conversion, since slow pages lose buyers regardless of ranking.

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In Ryze

The Page Speed Score in the Technical Audit is built from the same field data (CrUX). Pages with poor LCP, INP or TTFB for real users are listed as Warnings with a suggested fix. CLS is not part of the audit.

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Primary references