Core Web Vitals in plain terms: LCP, INP, CLS and what moves them
Google measures three things about how your pages feel to real visitors, and uses them in ranking. The names are unfriendly; the ideas are simple. Here is what each one means, what a good number is, what usually causes a bad one, and how to fix it.
Core Web Vitals are three measurements Google takes of how your pages feel to real visitors, collected from the Chrome browsers of people who actually visited. They are part of ranking, they appear in Search Console with red and orange bars, and they are explained everywhere in language designed for engineers. Here is the plain version.
The three numbers
Largest Contentful Paint, LCP. How long until the biggest thing on the screen, usually the main image or the headline, has appeared. It measures “when did the page show up”. Good is under two and a half seconds. Over four is poor.
Interaction to Next Paint, INP. When a visitor taps or clicks something, how long until the page visibly responds. It measures “does the page feel stuck”. Good is under two hundred milliseconds. Over five hundred is poor. This replaced an older measurement in 2024 and is the one most sites now fail.
Cumulative Layout Shift, CLS. How much the page jumps around while loading: the button that moves just as you tap it, the text that shifts when an image appears above it. Good is under a tenth. Over a quarter is poor.
Where to see yours
Search Console, under Experience, Core Web Vitals, shows which pages are good, need improvement or poor, grouped by cause. PageSpeed Insights shows the numbers for a single page, with the top section being the real-visitor data that counts. Numbers only appear once a page has enough visitors; small sites sometimes see nothing, which is not a pass.
What usually causes a bad LCP
- The server is slow to respond. Cheap hosting, no caching, old PHP.
- The main image is enormous, or loads late, or is lazy-loaded when it should not be.
- Render-blocking scripts and stylesheets that must finish before anything shows.
- Fonts that hide the text until they arrive.
Fix in that order. The server and the main image are usually the whole problem.
What usually causes a bad INP
- Too much JavaScript running on the page: page builders, trackers, chat widgets, sliders, each doing work on every interaction.
- Heavy third-party scripts that block the main thread.
- Menus and interactions built with more code than they need.
Fix: remove scripts that are not earning their place, defer the rest until after the page is interactive, and on sites built with heavy page builders, accept that the builder is the cause.
What usually causes a bad CLS
- Images and embeds without dimensions, so the page does not know how much space to reserve.
- Ads, banners or cookie notices injected at the top after the page has started showing.
- Fonts that swap and change the size of text.
Fix: give every image and iframe a width and height, reserve space for anything that loads late, and load fonts in a way that does not reflow the page.
How much it matters
It is one ranking signal among many, and a page with better content and better links will outrank a faster page with worse ones. But between two similar pages, the faster one wins, and the visitor effect is larger than the ranking effect: a page that takes five seconds to show loses a large share of visitors regardless of where it ranks.
What to do this month
Open the Search Console report. If everything is green, nothing. If pages are poor, look at which of the three numbers, find the cause from the lists above, and fix the biggest one first. Our scanner gives the outside view of the usual suspects: response time, image formats, compression, and whether a CDN is in front. Speed drifts as sites change, so this is a check we run monthly on every site we look after.
See where your own site stands.
The scanner checks the things this guide talks about, in about ten seconds, no signup.
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