WordPress Lighthouse: What is Time to First Byte?

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The Time to First Byte metric is measured as the time from the start of navigation request until the time that the client receives the first byte of the response from the server. It includes network setup time (SSL, DNS, TCP) as well as server-side processing.

You can find this metric and its evolution in the Speed Metrics tab of Lighthouse’s plugin settings.

The thresholds for fast/average/slow TTFB are 500 ms as the upper limit for fast TTFB and 1500 ms as the lower limit for slow TTFB.

  • fast TTFB < 500 ms is based on the server responsiveness best practice.
  • slow TTFB >= 1500 ms is based on the requirement for the fast Largest Contentful Paint (LCP) threshold to be < 1800 ms. A server response that exceeds 1500 ms will not, in most cases, meet the fast LCP goal.
WordPress Lighthouse Time to First Byte Metric
WordPress Lighthouse Time to First Byte Metric
WordPress Lighthouse Time to First Byte Evolution
WordPress Lighthouse Time to First Byte Evolution

The total time, in seconds, that the full pageload operation lasted, including connection and document return. This does not include any JavaScript, third-party resources or images. Also known as Raw Pageload Time, Time to First Byte (TTFB) or StartTransfer Time.

The TTFB is the total amount of time spent to receive the first byte of the response once it has been requested.

This metric is one of the key indicators of web performance. Google recommends this value to be between 250ms and 500ms.

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