Core Web Vitals: what to measure and what to ignore
A practical guide to the metrics Google actually weights in 2026.
Core Web Vitals are real ranking factors, but most explanations are overcomplicated. Here is the practical version.
The three metrics that matter
LCP — Largest Contentful Paint
How long until the biggest visible element on the page is rendered. Target: under 2.5 seconds.
Usually limited by: a large hero image, a slow font, server-side render delay.
Fix by: serving the hero image in modern formats (WebP, AVIF), preloading critical resources, hosting on edge infrastructure.
INP — Interaction to Next Paint
How long after a click or tap before the page visibly responds. Target: under 200ms.
Usually limited by: heavy JavaScript blocking the main thread.
Fix by: splitting JavaScript bundles, lazy-loading non-critical scripts, removing unnecessary dependencies.
INP replaced FID (First Input Delay) in 2024. INP is stricter — it measures the worst interaction, not just the first.
CLS — Cumulative Layout Shift
How much the page jumps around as it loads. Target: under 0.1.
Usually caused by: images without dimensions, late-loading ads or embeds, fonts swapping in.
Fix by: setting explicit width/height on images, reserving space for embeds, using font-display: optional or swap carefully.
What Lighthouse and PageSpeed Insights tell you
Both tools simulate page load and give you scores. Lighthouse is local (your machine, your network), PageSpeed Insights is Google's real data from real Chrome users (CrUX).
The score that matters for SEO is the CrUX score (the "Field Data" tab in PageSpeed Insights). That's what Google actually uses for ranking. Lighthouse is useful for catching regressions during development.
The diminishing returns trap
Once your site is green on all three metrics, additional optimisation rarely moves rankings. Studios that chase 100 Lighthouse scores are usually trading developer time for marginal gains. Get green, then move on to content.
When Core Web Vitals actually matter for ranking
Google uses Core Web Vitals as a tiebreaker when content quality is comparable. If your page is competing with another page on a tight margin, fast wins. If your content is much better, fast doesn't help and slow doesn't hurt.
This is why "make the site faster" alone is rarely a strategy. Pair it with content improvement and the gains compound.