Glossary

What is Time to First Byte (TTFB)?

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Time to First Byte (TTFB) measures how long until the browser receives the first byte from the server. It's a foundational metric - nothing can render until this completes.

Thresholds

ScoreRating
≤ 800msGood
800ms - 1800msNeeds Improvement
> 1800msPoor

Google recommends 800 milliseconds or less.

What TTFB Includes

  • Redirect time
  • DNS lookup
  • TCP connection
  • TLS negotiation
  • Server processing time

Sites with poor LCP have an average TTFB of 2,270ms - nearly consuming the entire 2.5s LCP budget.

Why It Matters

TTFB is the starting point for all other metrics. High TTFB delays FCP, LCP, and everything else. For SPAs, fast TTFB is especially critical since client-side rendering adds more time.

Common Issues

  • Slow server processing / database queries
  • No caching (regenerating cacheable responses)
  • Geographic distance without CDN
  • Too many redirects

Improve TTFB

  • Use a CDN
  • Enable caching at all levels
  • Optimize backend code
  • Use HTTP/2 or HTTP/3
  • Minimize redirects

Measure TTFB

  • Chrome DevTools Network panel ("Waiting for server response")
  • PageSpeed Insights
  • WebPageTest waterfall
TTFB is not a Core Web Vital, but directly impacts LCP which is. Slow TTFB makes good LCP nearly impossible.
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