Understanding Performance Metrics
Table of Contents
Speed testing measures how quickly your website loads and identifies performance bottlenecks. All tests run from your machine in the background.
Key Metrics Explained #
Time to First Byte (TTFB) #
The time it takes for the browser to receive the first byte of data from the server. Lower is better.
- Good: < 200ms
- Fair: 200-600ms
- Poor: > 600ms
Largest Contentful Paint (LCP) #
The time it takes for the largest content element (usually an image or text block) to become visible. This approximates perceived load time.
- Good: < 2.5s
- Fair: 2.5-4s
- Poor: > 4s
Total Blocking Time (TBT) #
The total amount of time that JavaScript blocks the main thread. High TBT means JavaScript is preventing interactivity.
- Good: < 200ms
- Fair: 200-600ms
- Poor: > 600ms
Load Time #
The total time to fetch all resources for the page.
- Good: < 2s
- Fair: 2-4s
- Poor:** > 4s
Page Size #
Total size of all downloaded resources. Larger pages take longer to load, especially on slower connections.
- Good: < 1MB
- Fair: 1-3MB
- Poor: > 3MB