Cumulative Layout Shift

---

Cumulative Layout Shift (CLS) quantifies visual stability by calculating how much elements within the viewport move around during page load. It helps pinpoint how often unexpected movement occurs on your pages. CLS is a Core Web Vital metric.

How to measure Cumulative Layout Shift?

The quickest and easiest way to see Cumulative Layout Shift performance for your site is to use our free Core Web Vitals test tool, or use the form below.

How is Cumulative Layout Shift calculated?

Cumulative Layout Shift is the sum of the largest, unexpected layout shift scores from all of the unstable elements during the lifespan of a page load. The layout shift scores are reported via the Layout Instability API and are a product of:

• distance fraction: the distance any unstable element has moved in the frame
• impact fraction: the surface area of the viewport that’s affected by unstable elements between two frames

Learn more in Cumulative Layout Shift: Measure and Avoid Visual Instability and web.dev guide to Cumulative Layout Shift calculation.

What Cumulative Layout Shift measurement is fast?

Pages with Cumulative Layout Shift lower or equal than 0.1 can be considered as fast, and recordings above 0.25 are considered slow.

Further resources

• Cumulative Layout Shift: Measure and Avoid Visual Instability
• Cumulative Layout Shift (CLS)
• Cumulative Layout Shift Debugger
• Chrome Speed: Cumulative Layout Shift Changelog