Updates on Google’s Cumulative Layout Shift

by Apr 23, 2021Blog

A layout shift happens when a page is unstable and shifts around, for example, not allowing you to click on a button since it’s constantly moving. You might have experienced this in a different form, such as trying to click on an article but instead clicking on an ad that randomly appears.

The following video, provided by Google, demonstrates a layout shift that will negatively affect the user.

A Cumulative Layout Shift (CLS) refers to a Core Web Vitals (CWV) metric calculated by summing all layout shifts that happen during the lifespan of a page and aren’t caused by user interaction. A layout shift occurs whenever a visible element changes its position from one rendered frame to the next one.

For a good user experience, websites should aim to have a CLS score of 0.1 or less. Anything more would suggest the page needs improvements. To calculate this score, the browser looks at the size of the viewport and the movement of unstable elements in the viewport between two rendered frames.

Cumulative Layout Shift scoring system

On the other hand, not all layout shifts are bad, especially when the user expects them. Layout shifts that occur in response to user interactions, such as clicking on a link or typing in a search box, would generally be fine. As long as the shift happens close to the interaction and the relationship is clear to the user.

Feedback for CLS from advertisers stated that it was an inadequate metric for measuring pages that are open for a long time, leading to a “bad” CLS score, which is why Google updated CLS to make it more accurate and fair.

From a list of solutions, Google has chosen to implement a Session Windows approach. According to Google, “A session window starts with the first layout shift and continues to expand until there is a gap with no layout shifts… When the next layout shift occurs, a new session window starts.”

Google also confirmed that most web pages wouldn’t see a change in their CLS scores, while about 42% of sites will see a slight improvement in scores. Another 3% of sites that use an infinite scroll or have user interface handlers that react slowly to user interaction will see their scores rise to a “good” rating.

This change is a good improvement for advertisers since web pages deserve an accurate and fair ranking system, especially now when CWV metrics are expected to become an SEO ranking factor in May 2021.

Don’t forget to listen to episode #52 of the #TWIMshow, where the speaker, Sajid, talks about other recent Google Ads updates. Feel free to book a no-obligation call today and speak to a Google Ads expert.