What is TTFB (Time to First Byte)?
TTFB measures how long your server takes to start responding to a request. Here's what it includes, what counts as a good TTFB, and why it matters.
The definition
Time to First Byte (TTFB) is the time between a browser requesting a page and receiving the first byte of the response. It covers the DNS lookup, the TCP and TLS connection setup, and — usually the biggest share — the time the server spends generating the response.
TTFB happens before anything renders. Every image, script, and stylesheet waits behind it, which is why a slow first byte drags every other speed metric down with it.
What counts as good
Common practice treats a TTFB under about 300ms as good and over about 800ms as slow. Dynamic pages (WordPress, e-commerce) naturally sit higher than static ones because the server does work on every request.
TTFB varies by visitor location: a server in Frankfurt answers a Paris visitor faster than one in Sydney. A single measurement is one vantage point, not a global truth.
What determines it
Three things dominate: how far the visitor is from the server, how fast the server generates the page (application code, database queries, caching), and the hosting infrastructure itself. Page-level optimizations — image compression, JavaScript bundling — don't touch TTFB at all.
Common questions
- Is TTFB a Core Web Vital?
- No. TTFB is not one of the three Core Web Vitals (LCP, CLS, INP), but it directly feeds LCP: the page can't paint content before the first byte arrives.
- What is a good TTFB?
- Under roughly 300ms is generally considered good; over roughly 800ms is slow. Dynamic sites typically sit between the two.
- Does TTFB affect SEO?
- Indirectly. Google's ranking systems use page-experience signals built on metrics like LCP, and a slow TTFB pushes LCP up.
Measure how fast your server responds, before any page code runs.
Check your TTFB →