What it is
Time to First Byte is the gap between a shopper’s browser asking for a page and the first piece of it arriving. It is the part of the wait that happens on your server, before any image or script is involved: the database query runs, the page is built, and only then does anything travel back. Everything else about page speed stacks on top of this number.
How common it is
Just over half of audited stores (55%) answer quickly enough. The audit measures the response time directly and passes it under 300 milliseconds, the threshold for a fast response. The rest sit higher, and because this delay lands before the page begins to render, no amount of image or script tuning further down can win the time back.
Why it costs you
Every shopper pays this wait before they see a single thing, on every page, every visit. A slow first byte means a blank screen for that whole stretch, and on a phone over mobile data it can run long enough that some shoppers leave before the store appears. The cause is usually the backend, an unindexed query, no full-page cache, or thin hosting, which is why a store can look well built and still feel slow to open.
Check it in 30 seconds
Run a product page through PageSpeed Insights (pagespeed.web.dev) and read the server response time, or open your browser’s Network tab and look at the “waiting” time on the first request. Much over half a second and your server is the bottleneck before anything else gets a chance.
Read next: Ecommerce Site Speed: Convert More of Your Traffic
Run the free audit to see how long your store makes shoppers wait before the page begins.