Low impact · weight 3 · worth up to 1.3 points of the total score
Images are usually most of a page's bytes. A photo straight from a camera or a design tool can weigh several megabytes when a few hundred kilobytes would look the same on screen, and every visitor on a phone downloads all of it. We ask each of the page's first ten images for its size, without downloading it.
Export photos at the size they are shown, in WebP or AVIF, at quality 75-85. Most CMSs and CDNs can do this automatically on upload.
Check a page for this, and the other 70 checks at once
Lighthouse performance score
Google's own composite of loading, interactivity, and visual stability, measured on a simulated mid-range phone. This is the number PageSpeed Insights puts at the top of its report.
Real visitors get a fast page
The Chrome UX Report measures Core Web Vitals on real Chrome users over the last 28 days, and it is the data Google's ranking uses, not the lab run. It exists only for pages, or whole sites, with enough traffic; when only the site has data, that is what this shows.
Largest Contentful Paint
LCP is the moment the biggest element in the viewport finishes rendering, which is when a visitor feels the page has arrived. Google's threshold for good is 2.5 seconds.
Cumulative Layout Shift
CLS measures content jumping around after it appears. It is why a visitor taps the wrong button when an ad or a late-loading image pushes the page down under their finger.
