Website performance should be measured through loading, responsiveness and visual stability, alongside the tasks visitors need to complete.
Understand the three metrics
Largest Contentful Paint measures loading, Interaction to Next Paint measures responsiveness and Cumulative Layout Shift measures visual stability. Google’s good thresholds are LCP at or below 2.5 seconds, INP at or below 200 milliseconds and CLS at or below 0.1, assessed at the 75th percentile. See the official Web Vitals guidance for definitions and measurement details.
Fix loading bottlenecks
Start with the main visible image and blocking stylesheets. Use suitable image formats, responsive sizes and explicit dimensions. Avoid lazy-loading the main hero image. Remove unused CSS with checks across all page families so performance work does not silently break a less common page.
Protect interaction and layout
Keep expensive scripts away from essential navigation and form handling. Reserve space for images and embeds. Test menu opening, typing and submission while other features are active. A fast initial screen does not establish whether the page stays responsive during use.
Compare lab and field evidence
Use lab tests to diagnose changes, then review real-user data when enough is available. Test several templates on mobile and desktop. Report the measurement method and conditions rather than treating one score as a permanent guarantee. Keep a baseline so new content and scripts can be checked for regressions.
