Core Web Vitals: LCP, INP and CLS
Core Web Vitals are Google's metrics for real-user experience, assessed at the 75th percentile of page visits (mobile and desktop).
Thresholds for the three metrics
| Metric | Measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP | Loading of the largest element | ≤ 2.5 s | 2.5 – 4 s | > 4 s |
| INP | Responsiveness to interactions | ≤ 200 ms | 200 – 500 ms | > 500 ms |
| CLS | Visual stability | ≤ 0.1 | 0.1 – 0.25 | > 0.25 |
INP replaced FID in March 2024. Check current thresholds on web.dev.
Measuring: field or lab?
- Field data (CrUX, Search Console, PageSpeed Insights): what your visitors experience; this is what counts for assessment.
- Lab data (Lighthouse, DevTools): reproducible, ideal to diagnose and test a fix.
Action plan
Start with the worst metric, then fix root causes: images (Images), server (Server), JavaScript (defer & async).
In this section
- LCPImprove LCP: the 4 sub-parts, LCP image with fetchpriority, preload, TTFB, CDN and critical CSS. Target ≤ 2.5 s.
- INPImprove INP: long JavaScript tasks, scheduler.yield, Web Workers, third-party scripts, DOM size and content-visibility. Target ≤ 200 ms.
- CLSReduce CLS: image dimensions, reserved ad space, font-display, injected content. Target ≤ 0.1.