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.
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.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.