---
title: Understanding Performance Metrics
description: "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…"
url: "https://ssh-assistant.com/docs/understanding-performance-metrics/"
updated: "2025-12-07"
category: Site Load Tester / Speed Tester
---

# Understanding Performance Metrics

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