Overview
Speed Index is a calculated score based on visual progress during page load. It represents the average time at which visible parts of the page are displayed. A lower score indicates a better user experience.
How it is Measured
Speed Index is typically measured using video capture of the page load. It calculates the visual completeness of the page over time and integrates the results to produce a single score.
Usage
Speed Index is a key metric in tools like Lighthouse and WebPageTest. It is particularly useful for comparing the perceived loading speed of different pages or designs.