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. Learn more in Time to First Byte: What it is and How to Make Improvements.

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?