CLS (Cumulative Layout Shift) - Definition

What is a CLS (Cumulative Layout Shift)?

Understanding CLS (Cumulative Layout Shift) in E-commerce

Quick Definition

Cumulative Layout Shift (CLS) is a critical web performance metric measuring visual stability by quantifying unexpected layout movements during page load. It calculates how much visible page content shifts without user interaction, directly impacting user experience and perceived website quality. Lower CLS scores indicate more stable, user-friendly web pages.

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Understanding Cumulative Layout Shift (CLS)

What is CLS?

Cumulative Layout Shift measures unexpected visual instability during webpage loading, tracking how much on-screen elements move without direct user interaction. A lower CLS score indicates a more stable, smoother user experience.

How CLS is Calculated

CLS = Sum of (Impact Fraction × Distance Fraction)

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Impact Fraction: Portion of viewport affected by layout shift
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Distance Fraction: Vertical distance elements move

Common CLS Causes

Unspecified Image Dimensions

Images loading without predefined width/height cause unexpected page shifts

Dynamic Content Insertion

Ads, recommendations, or late-loading elements pushing existing content

Web Fonts Loading

Custom fonts replacing default text can cause significant layout shifts

Embedded Content

Third-party widgets or iframes loading asynchronously

CLS Performance Benchmarks

CLS Score	Performance Rating
0-0.1	Good
0.1-0.25	Needs Improvement
0.25+	Poor

Optimization Strategies

To minimize CLS, implement strategies like reserving space for dynamic content, using size attributes for media, and leveraging CSS transform for animations. Tools like Growth Suite can help analyze and optimize page performance, ensuring smooth user experiences that support higher conversion rates.

Consistently monitoring and improving CLS contributes to better user engagement, reduced bounce rates, and ultimately, improved e-commerce performance.