What are Core Web Vitals?
Core Web Vitals are three Google-defined metrics that measure real-world page experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability). Together they gauge how fast, responsive and stable a page feels to the people using it.
Core Web Vitals, explained properly.
What Core Web Vitals actually measure
Core Web Vitals are a set of three metrics Google uses to describe how a page feels to a real person loading and using it. Each one isolates a different part of the experience. Largest Contentful Paint (LCP) measures loading: how long it takes for the largest visible element, usually a hero image or a block of text, to appear. It answers the question "has the main content shown up yet?". Google considers 2.5 seconds or faster to be good. Interaction to Next Paint (INP) measures responsiveness: how quickly the page reacts when someone taps, clicks or types. It replaced First Input Delay in March 2024 and looks at the full delay of interactions across the whole visit, not just the first one. A good INP is 200 milliseconds or less. Cumulative Layout Shift (CLS) measures visual stability: how much the layout jumps around while it loads. If a button moves just as you go to press it because an advert or image loaded late, that is layout shift. A good CLS score is 0.1 or below. The three are scored separately, and a page needs to pass all three at the 75th percentile of real visits to be considered as passing overall.
Why Core Web Vitals matter
They matter for two reasons that reinforce each other. First, Google uses them as part of its page-experience signals, which feed into ranking. They are not the single biggest factor, relevance and links still do the heavy lifting, but when other things are close, the faster, more stable page has an advantage. They also affect how easily crawlers and, increasingly, AI assistants can read and render a page. Second, and often more valuable, they map directly onto how buyers behave. A slow-loading page, a button that does not respond, or content that shifts under the cursor all cost you conversions regardless of where you rank. The revenue impact of the experience usually outweighs the ranking impact of the score. That is why the work pays twice: you win a little on visibility and more on the people who were already on the page.
How Core Web Vitals are measured
There are two kinds of data, and the difference matters. Lab data comes from a synthetic test on a single simulated device and connection, tools such as Lighthouse or the lab tab of PageSpeed Insights. It is useful for debugging because it is repeatable, but it is not what Google ranks on. Field data, also called Real User Monitoring, comes from the Chrome User Experience Report (CrUX): anonymised measurements from actual Chrome visitors on your real pages over a rolling 28-day window. This is what Google assesses, and it is reported per-page and per-URL-group in Search Console's Core Web Vitals report. The gap between the two is where most sites go wrong. A page can score well in a clean lab test and still fail in the field because real users are on slower devices, patchier connections and pages loaded with third-party scripts the lab never triggered. Any honest assessment starts with the field numbers.
Common misconceptions
A few things trip people up repeatedly. "A caching plugin will fix it." Usually not. Caching and similar plugins tend to improve the lab score without changing what a real user experiences. The genuine gains sit further back, in the images, fonts, scripts and the render path, and in how the site is hosted and delivered. Fixing those is harder, which is exactly why the shortcut is so tempting and so rarely works. "It is a one-off job." Performance regresses. A new template, a marketing tag, an unoptimised image uploaded by someone in a hurry, any of these can quietly undo months of work. Core Web Vitals need monitoring, not a single pass. "Perfect scores are the goal." The goal is passing the thresholds on the pages that matter and giving users a genuinely fast, stable experience. Chasing a flawless synthetic number past that point is effort spent where buyers will never feel it.
Core Web Vitals: common questions.
What are the three Core Web Vitals?
Largest Contentful Paint (LCP), which measures loading; Interaction to Next Paint (INP), which measures responsiveness; and Cumulative Layout Shift (CLS), which measures visual stability. A page needs to pass all three to pass overall.
What are good Core Web Vitals scores?
LCP of 2.5 seconds or faster, INP of 200 milliseconds or less, and CLS of 0.1 or below. Google assesses these at the 75th percentile of real user visits, so most of your traffic needs to meet them, not just a best case.
Are Core Web Vitals a Google ranking factor?
Yes, they form part of Google's page-experience signals. They are not the strongest factor on their own, but they help when other signals are close, and beyond ranking they directly affect conversion, which is often the larger prize.
Will a caching plugin fix my Core Web Vitals?
It usually improves the lab score without improving what real users experience. Genuine gains come from addressing the source: images, scripts, fonts, the render path and hosting. That is harder work but it is what actually moves both the field numbers and revenue.
What is the difference between lab and field data?
Lab data is a synthetic test on one simulated device, useful for debugging. Field data comes from real Chrome visitors over the previous 28 days and is what Google actually ranks on. A page can pass in the lab and fail in the field, so the field numbers come first.