I see that the TTFB is showing up as a “F” grade.
First Byte Time (back-end processing): 40/100
751 ms First Byte Time
156 ms Target First Byte Time
Which request is actually grabbing those #'s from? If I add up all the TTFB for all the request I get more than 756 ms TTFB. If I add up the first 2 requests, it’s lower than 756 ms TTFB.
The TTFB is for the page as a whole (from start of navigation until the first byte of the HTML). It will include any redirects as well It is the full time for the first request + everything up to the blue bar of the second request.
So it sounds I have to add request #1 (dns look up ms, initial connection ms, time first byte ms) and the request #2 (start off set ms, time first byte ms) to get to 750 ms. Please confirm.
Depends on what you are trying to do but basically find the first response that is a 200 response and then add the start offset to the first byte ms. The start offset is the absolute time in the waterfall where the request started so you wouldn’t want to go adding that to any earlier requests.