Google measures how your website feels to use with three numbers called Core Web Vitals. They sound technical, but each one describes something every visitor notices: how long the page takes to show up, how quickly it reacts, and whether it jumps around while loading.
This guide explains what the three numbers mean, what counts as a good score, how to check your own site for free, and what usually fixes a bad one.
The three measurements
| Metric | What it tells you | Good | Poor |
|---|---|---|---|
| LCP | How long until the main content is visible | 2.5 seconds or less | Over 4 seconds |
| INP | How quickly the page responds to a tap, click or key press | 200 milliseconds or less | Over 500 milliseconds |
| CLS | How much the layout shifts unexpectedly | 0.1 or less | Over 0.25 |
Largest Contentful Paint (LCP)
LCP is the moment the biggest thing on the screen, usually a headline or a main image, finishes appearing. It is the closest single number to “how fast did the page feel?”
Interaction to Next Paint (INP)
INP measures the delay between someone doing something, such as tapping a menu or pressing a button, and the page visibly responding. A page with poor INP feels sticky or frozen. INP replaced an older measurement called First Input Delay in March 2024.
Cumulative Layout Shift (CLS)
CLS measures how much content moves after it first appears. You have felt bad CLS if you have ever gone to tap a link and had an image or banner load above it, pushing the link down so you tapped something else.
What “passing” means. Google looks at real visits over the previous 28 days. A page passes when at least 75% of those visits were in the good range for all three measurements. Mobile and desktop are assessed separately.
Why they matter
There are two reasons, and the first is the important one.
Visitors notice. People leave slow pages, especially on phones. Every visitor who gives up before your page loads is one you paid to attract, through ads, SEO or word of mouth, and then lost.
Google uses them in ranking. Google has confirmed that Core Web Vitals feed into its ranking systems. Relevance still matters far more: a fast page that doesn’t answer the question won’t outrank a slower one that does. But when several pages are similarly useful, the better experience is an advantage.
How to check your site for free
- PageSpeed Insights. Go to pagespeed.web.dev and enter a page address. If your site gets enough traffic, the top of the report shows how real visitors experienced it. Below that is a simulated test with specific recommendations.
- Google Search Console. The Core Web Vitals report groups every page on your site into good, needs improvement and poor, so you can see whether a problem affects one page or a whole template.
Pay most attention to the real-visitor data. The simulated test is a diagnostic tool run on one device under fixed conditions, and it cannot measure INP at all because nobody is interacting with the page.
What usually causes poor scores
Slow LCP
- Oversized images. A photo straight from a camera or stock library can be many times larger than it needs to be. Resize it to the dimensions it is displayed at and save it in a modern format such as WebP or AVIF.
- Slow hosting. If the server takes a long time to respond, nothing else can start. Caching and a content delivery network help more than most people expect.
- Files that block the page. Large stylesheets, scripts and fonts loaded before anything is shown delay the first view.
Slow INP
- Too much JavaScript. Chat widgets, pop-ups, trackers, sliders and page-builder add-ons all compete for the browser’s attention. Remove the ones you don’t use and delay the rest until they are needed.
High CLS
- Images and embeds without dimensions. When the browser knows the size in advance it reserves the space. When it doesn’t, everything below jumps as the image arrives.
- Banners inserted at the top. Cookie notices, promotions and ads that push content down after it has appeared.
- Late-loading fonts. Text that changes size when a custom font arrives and reflows the page.
A sensible order of work
- Run your home page and your two or three most-visited pages through PageSpeed Insights on the mobile setting.
- Fix images first. It is usually the cheapest change with the biggest effect.
- List every third-party script on the site and remove the ones nobody can justify.
- Give every image and embed a width and height.
- Wait a few weeks, then check the real-visitor data again. It is a rolling 28-day window, so improvements take time to show.
If your scores are poor and the cause isn’t obvious, a performance review will pin down exactly what is slowing each page and what to do about it.