Time to First Byte


Time to First Byte (TTFB) is a a metric that reports the time between a request for a resource and the first byte arriving to the browser.

How is Time to First Byte calculated?

Time to First Byte is a sum of several request and networking phrases:

  • redirect time
  • service worker startup time (if present)
  • DNS lookup
  • connection and TLS negotiation
  • the request (until the first byte has arrived)

Because a slow response time can have a cascading, adverse effect on overall web performance, we recommend optimising Time to First Byte as a priority.

What Time to First Byte measurement is fast?

Good TTFB MeasurementPoor TTFB Measurement
≤ 800ms> 1.8s

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