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Cumulative Layout Shift

CLS measures unexpected visual movement of elements under the metric's rules.

Unexpected layout movement

  1. Before · text is in place
  2. After · new element pushes text
Illustration of movement, not a measured CLS score. Reserving space for images helps avoid this movement.

How it works

Reserve space for images and dynamic content; inspect changes during real interactions.

Example

Example: An image without reserved dimensions moves a button when it loads.

Common mistakes

Not every movement is an unwanted layout shift.

How can you check this in practice?

Record which elements move after loading. Reserve dimensions for images, ads and inserted content; also inspect fonts. CLS is unitless rather than a time value; the good threshold is ≤0.1 when assessing real visits.

Distinctions and limitations

Not every movement contributes to CLS: it has rules for unexpected shifts and interactions. A transform animation is not equivalent to a layout change pushing neighbouring text.

Official sources

Editorial responsibility: Martin Zhelyazkov · Founder of Z-Consult

Updated: 05/11/2026

For a correction or question: office@z-consult.bg