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Page speed

Page speed is how quickly a web page loads and becomes usable for a visitor, measured on real visits or in a simulated test.

How it works

A page loads in steps: the first byte from the server, the first content, the main content such as the product photo, and the response to taps. Each step has its own metric, so page speed is never a single number: always ask which metric, which device and whose visits. For a store, what counts are the product and category pages that ads and search results lead to. Speed matters after the click, when the ad is already paid for. What to fix first: site speed for online stores.

Ways to calculate

  • Field data: real Chrome visits over 28 days, read at the 75th percentile. A page with too few visits gets the figure for the whole site, or none (About PageSpeed Insights).
  • Lab data: one simulated load in Lighthouse on a mid-range phone, scored 0–100. It is repeatable, so it suits finding causes (Why lab and field data can be different).
  • Google Ads: a mobile speed score from 1 to 10 for page loading after mobile ad clicks (Metrics). In 2018 Google said the score is based partly on how speed relates to potential conversion rate (Google, 2018).

Example

Example store, not client data.

In the lab, the tableware shop’s crystal wine glass page scores 41 and shows the main photo after 5.2 s. Field data gives 2.3 s at the 75th percentile: three in four real loads show the photo within 2.3 s. One reason for the gap: the lab starts with an empty cache, while returning visitors may already have the files stored.

Not to be confused with

  • Core Web Vitals — three fixed metrics, each with a set “good” line; one of them measures loading. Page speed is broader.

Right and wrong readings

  • Wrong: “The lab score is 90, so the page is fast for our customers.” Right: the score comes from one simulated load. Google notes that good lab data does not necessarily mean a good experience for real visitors.

Benchmarks

Benchmark according to the HTTP Archive Web Almanac 2025 (Chrome UX Report data, millions of websites, July 2025): 62% of websites on mobile and 74% on desktop showed the main content within 2.5 seconds on at least three in four visits. These are websites of all kinds, not only stores: your niche may differ.

Sources