Google measures LCP, INP, and CLS using real visitor data, not lab tests. Your page has to pass all three thresholds at once, or it fails. Most sites don't know this.
Google measures Core Web Vitals by collecting data from real visitors on your actual site, not from controlled laboratory tests. The company evaluates three metrics, Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS), using the 75th percentile performance across both mobile and desktop visitors. This means one out of every four of your visitors is experiencing slower load times or janky interactions than Google's threshold, and that's the standard you're being graded on.
The critical rule most site owners miss: your page does not pass Core Web Vitals unless it meets the threshold for LCP, INP, and CLS all at the same time. Passing two metrics means your page fails. This is how Google actually grades your site for ranking purposes and customer trust signals.
Google collects real-user Core Web Vitals data for mobile and desktop independently. Your mobile site might pass all three metrics while your desktop version fails one, or vice versa. Each platform is evaluated at the 75th percentile of its own visitor base, so you need to optimize for both.
Businesses must meet all three thresholds for a page to pass Core Web Vitals, not merely achieve a high lab score.
Digital Silk, 2026
A page that fails Core Web Vitals loses ranking position in Google search results, appears less trustworthy to visitors, and experiences higher bounce and cart abandonment rates. Real-user performance data is the truth; optimizing only for lab tests or a single metric leaves money on the table. You need all three metrics passing at the 75th percentile to win on search and customer experience.
How WebKing runs this
We pull your actual visitor performance data across mobile and desktop, identify which of the three Core Web Vitals is dragging down your grade, and resolve the bottleneck so your page meets all three thresholds at once, the only way Google counts it as a pass.
Lab scores test your site in a controlled environment, but Google actually grades you on how real visitors experience it. Real-user data at the 75th percentile is what determines your ranking and customer perception, so a good lab score doesn't guarantee a passing grade.
You must pass all three thresholds, LCP, INP, and CLS, at the same time. Passing two out of three means your page still fails the Core Web Vitals check, which hurts your ranking and customer trust.
The 75th percentile captures real-world performance during peak traffic and slower connections, not cherry-picked ideal conditions. It's a harder standard, but it ensures your site works for the customers who need it most.
Lab tests run on fast connections and new browsers, but real visitors come from slower networks, older devices, and high-traffic periods. Real-user data reveals the actual bottleneck that lab tests miss.
Sources
The Lab is original analysis by WebKing. We summarize and interpret developments from the sources above for industrial, commercial, and small business owners. Figures are reported as published by their sources.
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