How to check your website speed, and what the numbers mean

Core Web Vitals are Google’s three measures of how a page feels to load and use.

• Largest Contentful Paint, or LCP, is the time until the largest thing on screen has appeared, usually the main image or the headline. Good is 2.5 seconds or less.
• Interaction to Next Paint, or INP, is the delay between a tap, click or key press and the page visibly responding. Good is 200 milliseconds or less.
• Cumulative Layout Shift, or CLS, is how far content jumps about while the page loads. Good is a score of 0.1 or less.

Google judges each one at the 75th percentile, which means three visits in four have to meet the mark.

PageSpeed Insights, at pagespeed.web.dev, is Google’s free test. Enter a page address and read the two halves of the result separately.

The top half is field data: measurements from real Chrome users over the previous 28 days. It appears only when a page or site has enough visitors, and it is the data Google itself uses.

The lower half is a lab test: one simulated visit on a mid-range phone. It gives the score out of 100 and a list of causes. Use it to find what to fix, and use the field data to judge the result.

Test the home page, one main service or product page and one article, all on the mobile tab. Different templates behave differently, and Google indexes the mobile version of a site.

PageSpeed Insights tests any public address, so the same three page types can be run for each competitor. Field data shows what their visitors experience. Where a competitor has none, compare lab results, which are run under the same simulated conditions for everyone.

Search Console’s Core Web Vitals report sorts every page it has data for into good, needs improvement and poor, separately for mobile and desktop. It shows whether a problem belongs to one page or to a template shared by hundreds.

Each number has its usual causes.

• LCP: compress the main image and serve it at the size it is shown, in a modern format, and stop scripts and stylesheets from holding up the first paint. Slow hosting shows here too.
• INP: cut the JavaScript the page runs, starting with third-party tags such as chat widgets, trackers and embedded tools.
• CLS: give every image and embed its width and height, and reserve space for anything that arrives late, such as banners and web fonts.

A page that passes all three and still loses is losing on something else: relevance, content or links. Speed removes a handicap and does not replace the answer. The wider comparison is set out in why a competitor outranks you, and how to check.