LCP, INP, CLS explained without jargon. How to measure them and what to do to go green in PageSpeed Insights.
Google measures the real experience of users on your website. Not yours when you check it from the office on 600Mbps fibre. That of real users, on real devices, with real connections. And the data it collects is used for ranking.
This started in 2021. In 2026, most SME websites still fail these metrics.
LCP — the largest element
How long it takes for the largest element on screen to appear. Usually the hero image or main headline. Good: under 2.5s. Bad: over 4s.
The most common culprit: an unoptimised 2-4MB JPEG hero image. The solution: WebP, correct dimensions, `loading="eager"` and `fetchpriority="high"` on that specific image.
INP — the response to interactions
Here is the most important change. In 2024, Google replaced FID (which only measured the first interaction) with INP, which measures all interactions throughout the entire session. Clicking a menu, pausing while scrolling, filling in a field. Everything. Good: under 200ms. Bad: over 500ms.
The usual cause of high INP: too much JavaScript blocking the main thread. Reduce bundle size, defer third-party scripts, and use Server Components where possible.
CLS — elements that shift
That moment when you are about to click a button and it shifts just before because a banner loaded above it. That is CLS. Good: under 0.1. Bad: over 0.25.
Most common cause: images without defined dimensions, dynamically inserted content, web fonts that change the layout when they load.
How to measure them
PageSpeed Insights uses real data from the Chrome User Experience Report. If your site has low traffic and real data does not appear, use Lighthouse in Chrome DevTools or WebPageTest for lab data. Google Search Console shows the aggregate of all your traffic in the "Page experience" section.
What changes when you go green
In projects where we have taken websites from red/orange to green: rises of 3-12 positions on competitive keywords. Not the only ranking factor, but when content and links are equal with competitors, Core Web Vitals break the tie.
Have a project in mind?
Tell us what you want to achieve.