Accept a website’s speed on field Core Web Vitals at the 75th percentile, not on one lab score

Google’s Core Web Vitals are LCP, INP and CLS, and a page passes when it meets all three targets at the 75th percentile of real page loads. Lab tools such as Lighthouse cannot measure INP, so a lab score alone cannot prove the result.

Source facts

According to web.dev, the Core Web Vitals are Largest Contentful Paint for loading, which should occur within 2.5 seconds; Interaction to Next Paint for interactivity, which should be 200 milliseconds or less; and Cumulative Layout Shift for visual stability, which should be 0.1 or less. The recommended measure is the 75th percentile of page loads, segmented across mobile and desktop, and a page passes when it meets all three targets at that percentile.

Lab tools that load pages without a user, such as Lighthouse, cannot measure INP; Total Blocking Time is offered as a lab proxy instead. The page states that lab measurement is not a substitute for field measurement and strongly recommends that sites set up their own real-user monitoring, because Chrome User Experience Report data lacks detailed per-pageview telemetry. INP replaced First Input Delay as a stable Core Web Vital in 2024.

Applicability

Use this for any public website or web application whose owner wants measurable speed and stability. The Chrome User Experience Report powers the field data shown in PageSpeed Insights and Search Console’s Core Web Vitals report.

DSE recommendation

DSE recommends writing field Core Web Vitals at the 75th percentile, split by mobile and desktop, into the acceptance criteria for website projects. Capture a baseline before the change, add real-user monitoring with the web-vitals library or an analytics tool that records the same metrics, and use Lighthouse and Total Blocking Time during development to catch regressions early rather than as the final proof.

Verification

After launch, compare the field LCP, INP and CLS at the 75th percentile with the baseline for the main templates, on mobile and desktop separately. Treat a page as accepted only when all three metrics meet their thresholds, and keep the report with the release record.

Official reference

web.dev — Web Vitals. Reviewed October 18, 2026.