Web performanceSEP 30, 20261 min read

Core Web Vitals: the three metrics that decide how fast a page feels

Core Web Vitals: the three metrics that decide how fast a page feels

Core Web Vitals are a set of metrics proposed by Google to measure real-world user experience on a website, covering three aspects: loading, interactivity and visual stability.

The three metrics and their good thresholds

According to web.dev: Largest Contentful Paint (LCP) should be at most 2.5 seconds; Interaction to Next Paint (INP) at most 200 milliseconds; Cumulative Layout Shift (CLS) at most 0.1. A page passes when, at the 75th percentile of visits, measured separately for mobile and desktop, all three metrics fall within the good range.

What to do first

Optimize the hero image, load fonts without blocking rendering, declare dimensions for images and ad slots to avoid layout shifts, and reduce JavaScript on the main thread to improve INP.

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