Google measures three things about how a website feels to the people using it: how fast the main content appears, how fast the page reacts to a click, and how much elements “jump” while it loads. They're called Core Web Vitals. They're not the only thing Google uses to rank results, but they are a real signal, and visitors feel every one of them.
What you'll achieve
- know what each of the three numbers measures and what a good value is;
- see your real numbers, from actual visitors;
- know where a poor value usually comes from.
The three numbers
| Metric | What it measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | how long it takes for the largest visible element to appear: the big photo, the heading, a block of text | up to 2.5 s | 2.5–4 s | over 4 s |
| INP (Interaction to Next Paint) | how fast the page responds when you click, tap or type | up to 200 ms | 200–500 ms | over 500 ms |
| CLS (Cumulative Layout Shift) | how much the content moves while the page loads | up to 0.1 | 0,1–0,25 | over 0.25 |
Google looks at the value for 75% of visits: if three quarters of visitors get an LCP under 2.5 seconds, the page's LCP is “good”.
Two kinds of measurements
- Field data: it comes from real visitors using Chrome, collected over the last 28 days. This is what counts for Google. A new website or one with few visits may not have enough yet.
- Lab data: a test run right now, from a single simulated device. It's good for finding the cause and seeing the effect of a change immediately. The 0 to 100 score in PageSpeed Insights comes from the lab.
If the two disagree, trust the field data.
The steps
A. See your numbers
- Open https://pagespeed.web.dev and enter the page address, for example your home page.
- At the top you see the result for mobile; the tab next to it is for desktop. Start with mobile: that's usually where the problems are, and where most visitors come from.
- The first section shows the field data for LCP, INP and CLS, if available. Below it is the lab test, with the score and the list of recommendations (Diagnostics).
- Repeat for 2–3 important pages: a service page, a product page, the contact page.
B. Track them over time
- In Search Console (see Google Search Console: connect your website to Google), the Core Web Vitals report groups your website's pages into good, needs improvement and poor, separately for mobile and desktop.
- After a fix, the report updates gradually as new data comes in from visitors, that is, over a few weeks.
C. Find the cause
Poor LCP — the main content appears late:
- the big image at the top of the page is too heavy or in an old format (see WebP and AVIF images: the same look, fewer kilobytes);
- the big image is lazy-loaded (
loading="lazy"); the first image must load immediately (see Images in WordPress: size, format and loading); - the server responds slowly: the page isn't cached, the PHP version is old, or there are too many plugins (see Slow website: what to check, in order);
- external fonts and scripts that hold the page back.
Poor INP — the page reacts slowly to clicks:
- too much JavaScript: sliders, animations, chat widgets, ad pixels, page builders;
- third-party scripts (chat, reviews, maps) that run on every click.
Poor CLS — the content jumps:
- images without width and height in the code, so the page doesn't reserve their space;
- banners, ads or the cookie bar pushing content down after it has loaded;
- fonts that swap after loading and change the length of the text.
What's realistic for a small website
- A lab score of 100 isn't the goal; all three numbers being “good” for real visitors is.
- Most of the gains come from three places: images, caching and the number of external scripts.
- A bigger hosting plan won't fix a heavy page. If the page is slow even with a single visitor, the cause is usually in the page, not the server.
If something doesn't work
- PageSpeed says there is no field data. The page has too few visits from Chrome. Use the lab test and follow the Search Console report as your visits grow.
- The score differs from one test to the next. That's normal for the lab test: it depends on the network and the load at that moment. Run it 2–3 times and look at the trend.
- Everything is green on desktop and red on mobile. The mobile test simulates an average phone on a slower network. Start from the recommendations on the mobile tab.
- You don't know what to change first. Send us the page address and we'll go through the report together.