Core Web Vitals(CWV)

Long definition

Core Web Vitals is the subset of page experience metrics Google has decided to treat as ranking signals. The set has evolved: FID (First Input Delay) was replaced by INP in March 2024 because FID measured only the first interaction, missing most of the real frustration. The current three are:

• LCP — Largest Contentful Paint. Time from navigation start to the largest in-viewport element rendering. Good: ≤ 2.5 s.
• INP — Interaction to Next Paint. Worst interaction latency observed during the visit. Good: ≤ 200 ms.
• CLS — Cumulative Layout Shift. Sum of unexpected layout shifts during the visit. Good: ≤ 0.1.

Google evaluates CWV on field data (real users in the wild, collected via the Chrome User Experience Report — CrUX) at the 75th percentile. Your lab-measured Lighthouse scores are useful for debugging but don't directly drive rankings.

A page passes CWV when all three metrics are in the good band at p75 over a rolling 28-day window for a meaningful volume of visits. Below that volume (roughly < 100 visits / 28 days), CrUX reports no data and CWV is not a ranking signal for that URL — Google falls back to origin-level data.

Common misconceptions

• "CWV is a top-3 ranking factor." It's a real signal, but a small one. A page with great CWV and weak relevance still loses to a page with mediocre CWV and strong relevance.
• "Lighthouse score is what matters." Lighthouse is lab-measured on one synthetic connection. Google uses field data from real users. You can have a 100 in Lighthouse and fail CWV because your real users are on slow networks or old devices.
• "CWV is per-page." Google prefers page-level data when available, but rolls up to URL-group or origin-level when CrUX traffic is too sparse. Small sites effectively rank on origin CWV.
• "CLS only matters during load." CLS is measured throughout the visit, including late-loading ads and async content that reflow the DOM.