---
title: "What is time to first byte (TTFB)?"
description: "TTFB measures server response time. Learn what it is, thresholds, and how to optimize it."
canonical_url: "https://unlighthouse.dev/glossary/ttfb"
last_updated: "2026-08-10T04:33:22.416Z"
---

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

<table>
<thead>
  <tr>
    <th>
      Metric
    </th>
    
    <th>
      Good
    </th>
    
    <th>
      Needs Improvement
    </th>
    
    <th>
      Poor
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      <strong>
        Core Web Vitals
      </strong>
    </td>
    
    <td>
      ≤ 800ms
    </td>
    
    <td>
      800ms - 1800ms
    </td>
    
    <td>
      > 1800ms
    </td>
  </tr>
  
  <tr>
    <td>
      <strong>
        Lighthouse Audit
      </strong>
    </td>
    
    <td>
      < 600ms
    </td>
    
    <td>
      600ms - 1200ms
    </td>
    
    <td>
      > 1200ms
    </td>
  </tr>
</tbody>
</table>

Aim for a field score of 800 milliseconds or less at the 75th percentile to pass the [Google threshold](https://web.dev/articles/ttfb). However, the Lighthouse audit requires a server response time under **600ms** to pass the lab check.

## What TTFB includes

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

Sites with poor [LCP](/glossary/lcp) have an [average TTFB of 2,270ms](https://almanac.httparchive.org/en/2024/performance) - nearly consuming the entire 2.5s LCP budget.

## Why it matters

TTFB is the starting point for all other metrics. High TTFB delays [FCP](/glossary/fcp), [LCP](/glossary/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](https://pagespeed.web.dev/)
- WebPageTest waterfall

<note>

TTFB directly impacts [LCP](/glossary/lcp), a Core Web Vital. Slow TTFB makes good LCP nearly impossible.

</note>