You’ve probably visited a website where something annoying happens; you’re about to click a button, but suddenly the page shifts and you end up clicking something else.
That’s what we call Cumulative Layout Shift, or CLS for short. It’s one of the most frustrating things for users, and it can hurt your site’s performance and SEO, too.
We’ll walk you through what CLS means, how it works, why it matters, and most importantly, how you can fix it. Let’s make your website smoother and friendlier for everyone.
What Is Cumulative Layout Shift?
Cumulative Layout Shift is a Core Web Vitals metric from Google. It tracks how much visible content on your page shifts around while it’s loading. These shifts usually happen when images, ads, or fonts load in after the text, and push things around unexpectedly.
For example, imagine you’re reading a news article and suddenly a banner ad loads at the top of the page. The paragraph you were reading jumps down. That jump? That’s a layout shift. This on-page SEO element measures how often and how much that happens.
How Is It Measured
CLS is calculated based on how many elements move on the screen and how far they move. The two key things it looks at are impact fraction (how much space the shifting element takes up) and distance fraction (how far the element moved).
So if something big shifts a lot, your CLS score will be high. A high CLS score means your users are likely getting frustrated with your site. And when users get annoyed, search engines take note.
Why Cumulative Layout Shift Is Important
Layout shifts aren’t just a minor inconvenience. They affect user trust and how people interact with your website. Here’s why CLS matters:
- Hurts User Experience: Unexpected movements can make your site feel glitchy and annoying.
- Lowers Conversion Rates: If users click the wrong button or leave your site, you lose potential sales or signups.
- Affects SEO Ranking: Google considers CLS as part of its page experience signals for ranking.
- Bad for Accessibility: Layout shifts can make your site harder to navigate for people with disabilities.
- Reduces Engagement: When people get annoyed, they stop scrolling and leave the page sooner.
What’s a Good CLS Score?
A good CLS score is 0.1 or less, and it should be measured using real-world data from the Chrome User Experience Report (CrUX). That’s data from real users on Chrome who have agreed to share performance info.
Here’s how Google classifies CLS scores:
- Good: 0.1 or lower
- Needs Improvement: Between 0.1 and 0.25
- Poor: Over 0.25
To hit a good score, at least 75% of your page loads should be at or under 0.1. The lower your CLS, the better your page feels for your visitors.
How to Measure CLS
There are two main ways to measure CLS: field data and lab data. Let’s look at both.
Field Data (Real User Data)
Field data comes from actual users who visit your website. Tools like PageSpeed Insights, Google Search Console, and Chrome User Experience Report (CrUX) help gather this info.
This is the most accurate way to measure CLS because it reflects what real people experience. However, it takes time to gather enough data, especially if your site doesn’t get a lot of traffic.
Lab Data (Simulated Testing)
Lab data is collected using tools like Lighthouse, WebPageTest, or Chrome DevTools. These tools simulate loading your page on a test device with set conditions.
While lab data gives you immediate feedback, it doesn’t always reflect real-world scenarios. Still, it’s super useful when you’re building or testing changes to your site before launching them.
How To Improve CLS
Check out these SEO techniques to improve CLS and increase organic traffic:
Leave Room For Images, Videos, And Iframes
One big reason pages shift is when images or videos load in without a set size. To avoid this, always define the width and height of media elements for smooth website navigation. This way, the browser knows how much space to reserve while loading.
If you use responsive images, make sure they still reserve space properly using aspect ratio boxes or CSS rules.
Tweak Fonts To Load Smoothly
When custom fonts load, they can change how the text looks and how much space it takes up. This is called a flash of unstyled text (FOUT) or flash of invisible text (FOIT).
Use font-display: swap in your CSS so that the browser shows a fallback font first, then swaps it with your custom font once it’s ready. This helps keep the layout stable.
Use Animations That Don’t Shift Layout
Avoid using animations or transitions that affect layout properties like height, width, margin, or padding. These can cause things to move around unexpectedly.
Instead, stick to animations that change opacity or transform (like fade-ins or slide-ins); they don’t trigger layout shifts and still look smooth.
Make Sure Your Pages Work With bfcache
Browsers use something called bfcache (back/forward cache) to instantly load pages when users hit the back or forward buttons. But if your site has scripts that unload or reload things, you may not benefit from bfcache.
To help with CLS, make sure your pages don’t reset layouts or reload media when users come back. Keep things stable so the experience feels seamless.
Conclusion On What Is Cumulative Layout Shift
Cumulative Layout Shift might sound technical, but it’s just about making your website feel smooth and stable. When things move around too much, users get frustrated, and that hurts your SEO and business.
So, take action today to test and improve your CLS score. A little effort now can lead to happier users and better rankings.
To take your website performance to the next level, let BestSEO help. Our SEO services are designed to improve your site’s speed, user experience, and visibility. Reach out to our team to optimize your performance and grow your traffic the smart way.
Frequently Asked Questions Cumulative Layout Shift
What Causes a High CLS Score?
Common causes include images or ads without set dimensions, dynamic content loading, and custom fonts changing the layout.
How Do I Check My CLS Score?
You can check it using PageSpeed Insights, Google Search Console, or tools like Lighthouse and Chrome DevTools.
Can CLS Affect My Search Ranking?
Yes, CLS is part of Google’s Core Web Vitals, which impacts your page experience score and overall ranking.
What Is a Good CLS Score to Aim For?
A good score is 0.1 or less on at least 75% of your page loads, based on field data.
Does Mobile CLS Matter More Than Desktop?
Both matter, but mobile usually sees more layout shifts, so it’s especially important to optimize for mobile users.
