How to Measure and Fix Cumulative Layout Shift (CLS)

Your website visitors are clicking away because your page is moving. Cumulative Layout Shift (CLS), that’s the technical measure of unexpected element movement, is costing you money. Good news? You can fix it. Aim for a CLS score of 0.1 or lower, and your users will actually stick around.

Here’s why this matters: Google counts CLS as part of its core web vitals, the metrics it uses to rank websites. Meanwhile, your real-world visitors are frustrated because buttons shift, text jumps, and images load in the wrong place. One frustrating interaction can destroy trust. Multiply that across thousands of visitors, and you’re looking at lost conversions.

This guide walks you through exactly how to measure CLS and fix it, with real numbers and actionable steps you can implement today.

What Is Cumulative Layout Shift? The Simple Definition

Picture this: you’re reading an article on your phone. You’re about to click a link when, suddenly, the entire text block moves down three inches. You accidentally tap an ad instead. Annoyed? That’s CLS in action.

CLS measures how much your page elements move unexpectedly while it’s loading. An image pops in late and pushes text down. An ad loads and shifts your navigation. A font swaps and resizes everything. Each movement counts toward your CLS score.

The higher your CLS, the worse the user experience. We’re talking about trust issues. When a page feels unstable, visitors leave. Studies show that sites with high CLS scores lose about 10% more conversions than those optimized for stability. Think about your own browsing habits ,  you probably abandon sites that feel janky, right?

And here’s what’s wild: most CLS problems are preventable. They’re not mysterious. Usually, it’s just poor planning on the development side. But we’ll get into that.

Measuring CLS: Where to Look and What Tools to Use

Start with Google’s Free Tools

The easiest place to begin is Google PageSpeed Insights. Go there, plug in your website URL, and scroll down to the Core Web Vitals section. You’ll see your CLS score right there, flagged as green (0–0.1, good), yellow (0.1–0.25, needs work), or red (above 0.25, fix it now).

Google Search Console also shows your CLS data across real user sessions. This isn’t theoretical ,  it’s what actual humans on your site are experiencing. Check the Core Web Vitals report under “Enhancements” to see which pages are struggling.

Lighthouse, Google’s built-in auditing tool, is available right in Chrome DevTools. Run an audit on your desktop and mobile versions separately. You’ll get a detailed breakdown of which elements are shifting.

Check Real User Metrics

PageSpeed Insights shows lab data (simulated), but Chrome UX Report (CrUX) shows real behavior. This is more reliable because it’s based on millions of actual user sessions. If CrUX shows your CLS is worse than PageSpeed suggests, you’ve got a real problem on your hands.

Tools like WebPageTest and GTmetrix give you visual filmstrips of your page loading. You can literally watch where the shifts happen. WebPageTest even lets you test on different devices and connection speeds, which matters because CLS can vary wildly between desktop and mobile.

The Visual Check Nobody Does

Load your page. Actually look at it. Watch carefully as everything appears. Do images jump? Does text reflow? Do buttons shift position?

Most website owners never do this. They just trust their tools. But honestly, your eyes are a tool too. Load on mobile and desktop. Clear your cache so you see the full loading experience, not cached content. This is how your actual visitors see things.

The Usual Suspects: Why CLS Happens in the First Place

Images Without Width and Height

This is the biggest culprit, and it’s painfully simple to fix. When you upload an image without telling the browser its dimensions, the browser can’t reserve space. The image loads, and suddenly the entire layout shifts to make room. Sounds obvious? You’d be surprised how many sites still don’t do this.

Ads and Embeds That Appear Late

Ad networks are convenient but messy. They load asynchronously, meaning they show up whenever they feel like it. An ad placeholder sits empty, then BAM ,  an ad loads and pushes your content down.

Third-party scripts do this too. YouTube embeds, social media widgets, comment sections ,  they all pop in at unpredictable times.

Fonts Switching Styles

Web fonts are beautiful until they’re not. Your page loads with a system font first. Then your fancy Google Font loads. Suddenly, everything resizes. Text gets wider, line height changes, and layout shifts follow. Visitors don’t see the serif typeface they’re expecting ,  they see the movement.

Dynamic Content That Wasn’t Reserved

Pop-ups, banners, notifications, newsletter signup boxes. They appear after the page loads because your developers didn’t reserve space for them. The visible content gets pushed out of the way when they show up.

Forms and Buttons Loading After the Fold

Sometimes a form or button doesn’t load immediately because it’s connected to JavaScript. When it finally appears, it shifts everything above it. Your visitor’s carefully positioned scroll position just moved.

How to Fix Cumulative Layout Shift,  The Step-by-Step Breakdown

Step 1: Reserve Space Before Content Loads

This is rule number one. Always, always tell the browser how much space elements will occupy before they load.

For images, add width and height attributes directly in your HTML:

<img src=”hero.jpg” width=”800″ height=”600″ alt=”…”>

The browser now knows that area needs 800×600 pixels. It reserves that space. When the image loads, it fits perfectly. No shift.

For responsive designs, pair this with CSS aspect-ratio:

img {

  width: 100%;

  height: auto;

  aspect-ratio: 800 / 600;

}

The image scales to fit the screen, but the browser still knows the proportions. The space is reserved.

Step 2: Give Ads and Embeds Fixed Dimensions

Before that ad network loads anything, create a container with a fixed height and width:

<div style=”width: 300px; height: 250px;”>

  <!– Ad will load here –>

</div>

Now the ad loads inside that reserved space. No pushing. No shifting.

For YouTube embeds and other third-party content, same approach. Use a wrapper div with fixed aspect ratio.

Step 3: Handle Font Loading Properly

Use CSS font-display: swap. This tells the browser to show text immediately in a fallback font, then swap to your custom font when it loads. Users see content right away instead of waiting for text to appear.

@font-face {

  font-family: ‘Custom Font’;

  src: url(‘font.woff2’) format(‘woff2’);

  font-display: swap;

}

Avoid font-display: block unless you have a really good reason. Block makes text invisible while the font loads, which feels broken.

Step 4: Stop Pushing Content Down

Pop-ups, banners, and notifications need space too. Don’t inject them above existing content. Load them in a reserved container, or use CSS to push content naturally:

body {

  display: flex;

  flex-direction: column;

}

.banner {

  height: 60px;

  order: -1; /* stays at top */

}

.content {

  order: 0;

}

The banner stays at the top. Content doesn’t shift.

Step 5: Test, Measure, and Track

Run PageSpeed Insights again. Compare the before and after CLS scores. Most sites see improvements of 50% or more once they handle images and ads properly.

Set up Google Search Console alerts. Track your CLS monthly. This isn’t a one-time fix ,  it’s maintenance. New pages get added. New ads get implemented. You need to stay on top of it.

The Technical SEO Checklist Every Website Needs

A technical SEO expert will tell you that CLS is just one part of page experience, but it’s the visible, emotional part. Your visitors feel it. Here’s what needs to happen:

✓ Images: Every image has width and height attributes. 

✓ Aspect Ratio: Responsive images use CSS aspect-ratio. 

✓ Ads: All ad slots have fixed dimensions. 

✓ Embeds: YouTube, Twitter, and other embeds use wrapper containers. 

✓ Fonts: font-display: swap is applied. 

✓ Dynamic Content: Pop-ups and banners load in reserved space. 

✓ Testing: CLS checked on mobile and desktop. 

✓ Monitoring: Google Search Console tracked weekly or monthly. 

If you’re working with developers, this becomes your technical SEO checklist. Share it with them. Make it non-negotiable.

Real Impact: What Fixing CLS Actually Does for Your Business

Let’s talk numbers. A CRO consultant will tell you that user experience directly affects conversion rates.

One SaaS company reduced their CLS from 0.28 to 0.08 by fixing images and ads. The result? A 7% increase in form submissions within four weeks. For them, that was worth $50,000 in annual recurring revenue.

An e-commerce store that was experiencing high bounce rates on product pages fixed layout shifts and saw a 12% drop in abandonment. Users stayed longer, browsed more, bought more.

Google’s own research shows that pages with good CLS (0.1 or below) have 24% lower bounce rates compared to pages with poor CLS (above 0.25).

Here’s the chain reaction: Fix CLS → better user experience → visitors stay longer → Google ranks you higher → more organic traffic → more conversions. It’s not magic. It’s basic cause and effect.

And honestly? It’s one of the easiest Core Web Vitals to improve. Unlike Largest Contentful Paint (which sometimes requires server changes) or First Input Delay (which requires JavaScript optimization), CLS fixes are often simple HTML and CSS tweaks.

Quick Wins for Business Owners Who Want Results Fast

Don’t have weeks to redesign your site? Start here:

This week: Add width and height to all images on your homepage. Use bulk find-and-replace if you have to.

Next week: Check your ad network settings. Reserve space for those ad slots.

Week three: Audit your fonts. Switch to font-display: swap.

Week four: Test on mobile. This is where most CLS problems hide.

Ongoing: Check your CLS score monthly. Set a calendar reminder.

Most of these take 30 minutes to an hour if your site runs on WordPress or another CMS with basic HTML access. If you’re using Elementor, Divi, or similar page builders, the tools are built in.

Tools That Actually Help (Free and Paid)

Google PageSpeed Insights ,  free, no sign-up needed, tells you exactly what to fix.

Google Search Console ,  free, shows real user data, tracks progress over time.

Lighthouse ,  free, built into Chrome DevTools, super detailed.

Chrome UX Report ,  free, shows what real visitors experience.

WebPageTest ,  free basic version, paid pro features, visual filmstrips of page load.

GTmetrix ,  free and paid tiers, good for ongoing monitoring.

WordPress plugins like WP Rocket and Perfmatters have built-in CLS monitoring and often include one-click fixes for images and lazy loading.

Why Ignoring CLS Costs You Real Money

Every frustrated click-away is a potential customer gone. Every layout shift is a moment of doubt. Build that up across thousands of visitors, and you’re talking about lost revenue.

Google penalizes poor CLS in rankings. That means less organic traffic. That means higher customer acquisition costs. That means lower profit margins.

And then there’s brand perception. Sites that feel broken or unstable don’t inspire trust. Users remember that feeling. They tell their friends. Your reputation suffers quietly in the background.

But here’s the flip side: fix it, and you’re ahead of most competitors. Most websites have never even heard of CLS. You’ll be in the top 10% once you address it.

Final Thoughts: Make This a Habit, Not a One-Time Task

CLS isn’t something you fix once and forget. Every time you add an image, every time you integrate a new ad network, every time you add a pop-up, you risk creating layout shifts.

Treat it like website maintenance. Check it monthly. When something breaks, fix it immediately. It takes five minutes. It’s worth thousands.

Your visitors will notice. They’ll stay longer. They’ll come back. And Google will reward you for it.

Start today. Go to Google PageSpeed Insights. Plug in your URL. Look at your CLS score. If it’s above 0.1, you know what to do.

Next step: Check your CLS score right now. It takes two minutes. Once you know where you stand, everything else becomes a list of fixes, not a mystery.

Your website is losing traffic to layout shifts. But you can stop that today.

• December 31 , 2025
• Rushik Shah