The three current Core Web Vitals are Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). LCP measures how long the largest above-the-fold element takes to render. INP measures responsiveness to user input across the visit. CLS measures unexpected layout movement over the lifetime of the page. Google’s “Good” thresholds, measured at the 75th-percentile session, are LCP ≤ 2.5s, INP ≤ 200ms, and CLS ≤ 0.1, with “Needs Improvement” and “Poor” bands above each. INP replaced First Input Delay (FID) on March 12, 2024 as the responsiveness metric; FID is deprecated, though older writeups still cite it.
Two measurement systems coexist. Field data comes from the Chrome User Experience Report (CrUX) — real Chrome users on the site, 28-day rolling window — and is what Google uses for the ranking signal. Lab data comes from Lighthouse, a single synthetic run on a simulated device, useful for diagnosis but not the ranking input. The metric does double duty: it is a confirmed part of Google’s page experience signals for search ranking, and the underlying experience — fast paint, responsive taps, no shift under the buy button — correlates with conversion rate and bounce.
On a Shopify storefront, two CWV failure patterns show up most. Hero and PDP images without explicit width and height attributes inflate CLS. Liquid sections that hydrate third-party scripts — review widgets, live chat, social proof popups — inflate INP. Those are the pointers, not a tuning guide.