The three measurements
Largest Contentful Paint (LCP) is the time from the start of the navigation until the largest piece of content in view, usually a hero image or a block of text, has been drawn. Google calls 2.5 seconds or less good, and more than 4 seconds poor.
Interaction to Next Paint (INP) replaced First Input Delay in 2024. It looks at the delay between a tap, click or key press and the next frame the browser paints, across the whole visit, and reports one of the slowest. Up to 200 milliseconds is good; above 500 is poor.
Cumulative Layout Shift (CLS) adds up how far visible elements move unexpectedly while the page loads: an image without a reserved size that pushes the text down, or a banner that appears late. It has no unit. 0.1 or less is good; above 0.25 is poor.
Why the 75th percentile
A page does not have one speed. A visitor on a new laptop at home and one on an older phone on a train see very different numbers. Core Web Vitals are therefore judged at the 75th percentile: the value that three out of four visits beat. A page passes only when all three measurements are good at that point, so a fast median with a slow tail still fails.
Field data and lab data
Lab data comes from a tool such as Lighthouse that loads your page once under fixed conditions. It is repeatable and good for finding a cause, but it is one simulated visit. Field data comes from the browsers of real visitors, with their devices and networks, and it is what Google's own reports use. The two often disagree: a lab run cannot know that half your visitors are on mid-range phones, and it does not press buttons the way people do.
Why it matters for search
Google has said that page experience, including Core Web Vitals, is one of many signals in ranking. It is not a trump card: relevant content with a modest score outranks a fast page that answers nothing. Treat the vitals as a way to avoid being held back.
Measuring them on your own site
The measurements come from the browser, so an analytics script can collect them from real visits. trckable sends them along with an event it already sends, so there is no extra request, and shows the 75th percentile per page in the Speed table of Explore. See the features overview in the docs for where it sits.
Keep an eye on the pages that carry most of your pageviews: a slow page nobody visits matters less than a slow landing page.
Common fixes
- Give images and embeds a width and height, to stop layout shift.
- Serve the hero image at the size it is shown, and do not lazy-load it.
- Keep scripts that run on load small and deferred.
Try it in trckable
The Speed table in Explore shows Core Web Vitals at the 75th percentile, measured in the browsers that actually visited your pages. Read your dashboard
Related terms
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