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Last Reviewed: October 10, 2020

Performance Metrics

Overview of how and what to measure when optimizing your site for performance.

There are many different ways to measure page speed and performance. This guide will help you tune your site for the metrics in Google's Core Web Vitals, which focus on three aspects of the user experience—loading, interactivity, and visual stability.

These metrics include:

Loading Performance

LCP (Largest Contentful Paint) measures loading performance. Ideally, LCP should occur no more than 2.5 seconds after the page starts loading.

The amount of time it takes for a site to respond, Time To First Byte (TTFB), along with the time it takes a page to render meaningful content above the fold, Time To First Paint (TTFP), are both factors for Google's page rankings. All other qualifiers being equal, search rankings can drop by 5 or 10 if TTFB goes up a few hundred milliseconds.

Interactivity Delay

FID (First Input Delay) measures how long it takes before interaction with the page is possible. A FID of less than 100 milliseconds provides optimal user experience.

Visual Stability

CLS (Cumulative Layout Shift) measures visual stability, and helps quantify how often users experience unexpected layout shifts. Pages should maintain a CLS of less than 0.1.

To tune your site for these metrics, focus on these key areas: