Google has measured site speed for years, but since 2021 it has made three specific metrics official for judging the real experience of someone visiting a page: the Core Web Vitals. They aren’t abstract numbers for specialists: they measure concrete things like how long it takes before the main content is visible, or how much a page “jumps” while loading.
The three metrics
- LCP (Largest Contentful Paint) Measures how long it takes for the largest element on the page to appear, often an image or a heading. Good within 2.5 seconds.
- CLS (Cumulative Layout Shift) Measures how much the page shifts while loading, for example when an ad banner pushes down the text you were about to click. Good below 0.1.
- INP (Interaction to Next Paint) Measures how long the page takes to respond when someone clicks or taps something. Good within 200 milliseconds. It replaced the old FID (First Input Delay) in March 2024.
Why Google measures them
The three metrics come from observing what actually annoys people while browsing: waiting, watching the page move on its own, clicking something that doesn’t respond. They became a ranking factor, though with less weight than content quality and relevance to the search.
How to improve them without being a developer
For LCP, the most common cause is a featured image that’s too heavy: compressing it and converting it to WebP helps a lot. For CLS, the most frequent problem is images without declared dimensions, which make the layout “jump” once they finish loading. For INP, the cause is often too much unnecessary JavaScript running right at page load. A caching plugin helps all three metrics at once, as explained in the guide on how to speed up a WordPress site.
Where to check them
The most reliable way is PageSpeed Insights, which shows both real data collected from visitors (when available) and a lab estimate. Search Console’s “Page experience” section instead shows the trend over time across every page on the site, useful for understanding whether an issue affects a few pages or the whole site.
FAQ
Are Core Web Vitals the same on mobile and desktop?
No, they’re measured separately, because conditions differ: a slower connection and a less powerful device on mobile almost always lead to worse numbers than desktop.
Google gives more weight to mobile data for indexing, since most searches now happen from smartphones.
What replaced FID?
INP (Interaction to Next Paint), as of March 2024. The old FID only measured the delay of the very first click or tap on a page; INP measures responsiveness throughout the whole visit, not just the first interaction.
The change made the metric more representative of real experience, especially on pages where people interact multiple times, not just at the start.
Does a high Lighthouse score guarantee good Core Web Vitals?
Not always. The Lighthouse score is calculated in a lab, under controlled conditions; the “official” Core Web Vitals Google uses for ranking are instead real data collected from actual visitors, when there’s enough of it. We cover this in the guide on how to read your Lighthouse score.
The two usually point in the same direction, but they can differ on sites with very varied traffic or very different devices.
Do I need to be a developer to improve Core Web Vitals?
Not for the most common fixes: compressing images, a caching plugin, and removing unnecessary plugins cover most cases on WordPress sites.
For deeper issues, like too much custom JavaScript or a very heavy theme, you may need a developer’s help to work on the code itself.
How much do Core Web Vitals matter for rankings?
Less than many people think. Google has described them as one factor among many, with less weight than content quality and relevance to the search.
They’re still worth caring about: between two similar pages with comparable content, the faster and more stable one has an edge, on top of offering a better experience to visitors.
This article is for informational purposes. SEO results depend on many factors and timelines vary by site.