Short answer: Core Web Vitals are Google’s three page experience metrics: LCP measures how quickly the main content appears (good is up to 2.5 seconds), INP measures how quickly the page responds to a click or tap (good is up to 200 milliseconds), and CLS measures how much the content shifts while loading (good is up to 0.1). On WordPress, the biggest gains usually come from a lighter theme, fewer plugins, optimised images and caching.
Site speed is one of the few things that affects Google, ads and sales all at once. A slow page loses visitors before they see the offer, and Google Ads gives a slow landing page a worse quality rating. But not all speed is equal: Google looks at the experience of real users, through three specific metrics.
The three metrics Google measures
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | When the largest element appears: the hero image or a large heading | up to 2.5 s | over 4 s |
| INP (Interaction to Next Paint) | How quickly the page visibly responds to a click, tap or keypress | up to 200 ms | over 500 ms |
| CLS (Cumulative Layout Shift) | How much the content moves unexpectedly | up to 0.1 | over 0.25 |
INP replaced the older FID metric in March 2024. The difference is significant: FID only measured the first interaction, while INP measures responsiveness throughout the visit. That is why many sites that used to be “green” now have a problem, most often because of too much JavaScript.
Where to check
- Google Search Console, Core Web Vitals report: real-user data for the whole site, grouped by page type. This is what Google uses.
- PageSpeed Insights: for an individual page. The top section shows real-user data (if there is enough of it), the bottom section a lab test with recommendations.
- Chrome DevTools: for developers, the Performance tab shows exactly what is blocking the response.
Important: the 0 to 100 lab score is not what Google ranks on. A site can have a score of 70 and excellent real-user data, and vice versa.
The usual culprits on WordPress sites
Slow LCP
- A huge hero image, or a slider with several large images. Sliders are a frequent offender and rarely bring in sales.
- Slow hosting and no page caching.
- Fonts and CSS that block rendering.
- A main image that is lazy-loaded even though it is visible straight away.
Poor INP
- Heavy page builders and themes with lots of scripts.
- Too many plugins, each loading its own JavaScript on every page.
- Third-party scripts: chat widgets, several analytics tools, social media widgets, banners.
- Menus and filters that trigger expensive operations on every click.
High CLS
- Images and video without a set width and height.
- Cookie banners or notices that push content down.
- Fonts that change the size of the text once they load.
What to do, in order of payoff
- Page caching with a plugin that suits your server, for example LiteSpeed Cache on LiteSpeed hosting. Often the biggest single gain.
- Images: WebP or AVIF format, the right size for display, set dimensions, and lazy loading for everything except the first visible image.
- Plugin clean-up: remove the ones you do not use and check which scripts load on every page without need.
- Delaying third-party scripts until the user starts interacting with the page, especially chat widgets.
- Critical CSS and fonts: load what the visible part of the page needs first, and load fonts with font-display: swap.
- Theme: if the theme itself is heavy, no plugin will fully fix it. When redesigning, choose a lightweight base.
- Hosting: the server should be close to your users and run a modern version of PHP.
How much this affects rankings
Google says page experience is part of its ranking systems, but that relevant, helpful content matters more. Speed rarely lifts a page to the top on its own, but a slow page easily loses to an equally good competitor. The bigger effect is on conversions: a faster page brings more enquiries from the same number of visits.
Frequently asked questions
Do I need a score of 100 in PageSpeed?
No. The goal is green real-user data in Search Console. Chasing a perfect lab score often means sacrificing features that sell.
Why is the mobile result worse than desktop?
The test simulates a slower phone and a slower network. Since most visitors arrive on a phone, the mobile result is the one that matters more.
How quickly do changes show in Search Console?
Real-user data covers the last 28 days, so improvements appear gradually over several weeks.
Conclusion
Speed is not one number but three specific metrics, each with its own causes. The best results come from working in order: caching, images, plugins, scripts, theme. We check speed in every SEO audit and build it in from day one when we design and develop a website.
Related: WordPress security · SEO for a new website
