Cumulative Layout Shift

Cumulative Layout Shift

Cumulative Layout Shift is a measure of how much visible content on a page moves around unexpectedly while the page is loading or during use. It sums up the size and frequency of those shifts so you can tell how stable the layout felt to a visitor. Unexpected moves—like a button jumping down as an image loads—are frustrating and can cause users to click the wrong thing, lose their place, or abandon the page. The usual culprits are images or videos without reserved space, ads or embeds that insert themselves later, and web fonts that change text size unexpectedly. Reducing these shifts improves usability and trust because the page feels predictable and reliable. Easy fixes include specifying width and height for media, reserving space for third-party content, avoiding inserting new content above what a reader is viewing, and using font-loading strategies. Because this measure focuses on visual stability rather than raw speed, a page can be fast yet still score poorly if elements move. Maintaining steady layout makes interactions smoother and can help keep visitors on the page.