---
title: "What is TTFB? Time to first byte, explained — warmup.rocks Glossary"
description: "TTFB measures the time until the first response byte: DNS, TCP/TLS, network travel and server processing. What's inside the number, what counts as good, and why cache state dominates it."
canonical: https://warmup.rocks/glossary/ttfb
---

# TTFB (time to first byte)

**TTFB** is the time from starting a request until the first byte of the response arrives. It bundles everything that happens before any content can render: DNS resolution, TCP and TLS handshakes, the request's travel time, the server's thinking time, and the first byte's trip back. That makes it the single best indicator of whether a response came from a nearby cache or from a distant, busy origin.

## What's inside the number

1.  **DNS lookup** — resolving the hostname (often cached, sometimes not).
2.  **TCP + TLS handshake** — one to two round trips to wherever the connection terminates. With a CDN that's a nearby [PoP](https://warmup.rocks/glossary/point-of-presence); without one, your origin.
3.  **Server processing** — for a cache hit, a memory/disk lookup (milliseconds); for a miss, the full origin render: application code, database, templates.
4.  **First byte back** — one more one-way trip.

Note that tools measure slightly differently: browser metrics (CrUX, Lighthouse) count from navigation start including redirects; synthetic tools often report post-connection time. Compare like with like.

## What's a good TTFB?

Google's Core Web Vitals guidance treats **under 800 ms** as good and over 1,800 ms as poor — but a cached edge response typically lands **under 100 ms**. The gap between those two numbers is almost always cache state and distance: an edge hit skips the origin entirely, while a miss pays the origin round trip _plus_ render time. That's why the same URL can show a 50 ms TTFB in Frankfurt and 900 ms in Sydney — [each PoP caches independently](https://warmup.rocks/glossary/point-of-presence).

## Measure it properly

A single measurement from your desk samples one location with a possibly warm cache. The [global TTFB test](https://warmup.rocks/ttfb-test) measures from 8 locations at once, and the [website speed test](https://warmup.rocks/website-speed-test) shows first vs. repeat visit per location — the delta between them is your caching win. For the deep dive into diagnosing and fixing slow TTFB, see [our TTFB guide](https://warmup.rocks/blog/time-to-first-byte); for keeping edge caches warm so visitors never pay the miss penalty, that's [cache warming](https://warmup.rocks/blog/what-is-cache-warming).