Available in:
SyntheticCrUXRUM
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?#
Pages with Time to First Byte below or equal 800ms are considered as fast, and above 1800ms are considered slow.
Browser compatibility#
Time to First Byte is supported in all major browsers: Chrome, Edge, Firefox, and Safari. See full browser compatibility.