Understanding Key Web Performance Metrics: TTI, FID, and TBT Explained

Time to Interactive (TTI) measures how long it takes for a webpage to become fully interactive. In contrast, First Input Delay (FID) measures the time between a user's first interaction and the browser's response. Both metrics are crucial for performance evaluation.

First Input Delay (FID) gauges the delay between the user's initial interaction and the browser's response. This is closely related to Total Blocking Time (TBT), a lab-measurable metric that captures issues affecting page interactivity.

In coding, FID quantifies the duration between the content's initial paint (First Contentful Paint or FCP) and the website's readiness to process events. It helps developers optimize for responsiveness.

Although FID measures real-world user interactions, TBT is lab-measurable. While not identical, they are closely related and capture similar issues affecting a website's interactivity.

Time to Interactive (TTI) is different from First Contentful Paint (FCP). TTI gauges when a page becomes reliably interactive after FCP occurs, making it a more comprehensive performance metric.

In gaming, professionals aim for input delays under 15 milliseconds, while casual players find latencies under 40 milliseconds acceptable. Delays above 50 milliseconds can be bothersome.

Max Potential FID is a worst-case metric for First Input Delay. It identifies the longest possible delay between a user's interaction and the browser's response.

High input delay can be due to factors like high-resolution graphics or an overworked graphics card, underlining the need for optimizing settings.

First Input Delay can only be tested in real-world scenarios involving user interactions. Lab tools like Lighthouse report a related metric, Total Blocking Time (TBT), useful for initial assessments.

Input lag can affect not just competitive gaming but also general computer use. Higher lag becomes increasingly noticeable and problematic.