TTFB
Time to first byte measures how fast a server starts answering: DNS, connection setup, server processing and the first byte back.
Definitions only — a term explained here is not a service we sell.
Time to first byte is the wait between sending an HTTP request and receiving the first response byte. It covers DNS when the name is not cached, connection and TLS setup, the request upload, server processing and the trip back, but not the rest of the response.
Where the first byte waits
40 ms
| Value | What it means |
|---|---|
| 1 ms | Same metro |
| 10 ms | Regional path |
| 40 ms | Regional path |
| 120 ms | Intercontinental path |
| 300 ms | Queues or a long path |
| 800 ms | Queues or a long path |
Text description
The ruler runs from 1 to 1000 ms. Its six rows run from 1 ms in the same metro to 800 ms for queues and long paths. TTFB adds DNS, connection setup and server processing to that network time.
What the number hides
TTFB stops at the first byte, so it says nothing about the rest of the response or how the page renders. A fast TTFB with a slow body is still a slow page. A slow value can come from DNS, a cold cache, a redirect chain, a server queue or a distant site. Compare from the user's network, because a data-center check can miss the mobile path. The Ping tool shows the network leg.