# Performance metrics fundamentals — Web Performance Optimization

Source: https://www.geekswithgeeks.com/en/web-performance/web-perf-03

> Learn FCP, TTFB, FMP, and other key metrics that measure different aspects of loading and rendering.

## Time to First Byte (TTFB)

**TTFB** is the time from request to first byte of response. Includes network latency and server processing. Target: < 600ms. Optimize server response time and use CDN to reduce this metric.

## First Contentful Paint (FCP)

**FCP** marks when first content (text, image, or background) appears. Target: < 1.8 seconds. Critical for perceived load performance—users want to see something quickly.

## Time to Interactive (TTI)

**TTI** is when the page becomes fully interactive. Heavy JavaScript can delay this. Focus on reducing main thread blocking and ensuring responsive interactions after content loads.

## Metric relationships

Timeline: TTFB → FCP → LCP → TTI. Each metric builds on previous. Understanding this sequence helps identify bottlenecks. A high TTFB affects all downstream metrics.

Quick check

**Quiz:** What does TTFB measure?

- [ ] Time to first response byte
- [ ] Total transfer time
- [ ] Time to finish loading