What Core Web Vitals are
Google uses three numbers to measure a page's loading, responsiveness and visual stability:
- LCP (Largest Contentful Paint): how long it takes for the largest element on the page to appear, usually the main image or heading. Good is 2.5 s or less.
- INP (Interaction to Next Paint): how quickly the page responds to a click or typing. Good is 200 ms or less. It replaced the older FID in March 2024.
- CLS (Cumulative Layout Shift): how much the content unexpectedly jumps around, most often while loading. Good is 0.1 or less.
There are two kinds of data. Lab measurement (Lighthouse) simulates a single phone on a slower network and helps you find causes. Field data (Chrome UX Report) is collected by Google from real visitors over the last 28 days, but only for websites with enough traffic.
Why it matters for a small business
Most visits to business websites now come from phones, often over mobile data. When a page takes long to load or jumps under the visitor's finger, people go back to the search results and on to a competitor.
What slows websites down most often
- Large images: a full-resolution photo from a phone instead of a scaled-down version in WebP or AVIF format.
- Too many third-party scripts: chat, maps, analytics, ad pixels, sliders and CMS plugins.
- Slow hosting or no page caching, so the server takes long to respond.
- Static files without compression and without a cache lifetime set for the browser.
- Images and ads without dimensions, web fonts and a cookie banner that shift the content after loading.
What WebMeter checks, and what it doesn't
WebMeter has Google PageSpeed Insights measure your homepage 3× in the mobile view and takes the median. It assesses LCP, CLS, main-thread blocking (TBT, the lab counterpart of INP), server response and the overall Lighthouse score. It lists the biggest savings, static files without caching and an uncompressed page. If Google's field data misses the recommended Core Web Vitals values, WebMeter flags this as information that does not count towards the score.
It measures only the homepage, not subpages, the basket or logged-in areas. If PageSpeed Insights does not respond in time, the speed area is left out of the result.