Quick Shopify win: fixing CLS to boost your performance score
Many Shopify store owners focus on speeding up load times or removing heavy apps to improve site performance. While those are important, there’s one area that’s often overlooked - CLS, or Cumulative Layout Shift.
Fixing your CLS can be one of the quickest ways to raise your Google PageSpeed Insights (PSI) score, sometimes within an hour. It doesn’t always require a full site overhaul or removing key apps. Just a few precise code fixes can make a visible difference.
What CLS really means (and why it matters)
CLS measures how much the visible parts of your page shift as it loads.
You’ve probably experienced this before: you go to click a button, and right before your finger lands, the page moves. Suddenly you’ve clicked the wrong thing. That’s a layout shift.
Google tracks this using CLS as part of its Core Web Vitals. In PSI, it contributes 25% of your total performance score.
The breakdown looks like this:
CLS (Cumulative Layout Shift): 25% of your score
LCP (Largest Contentful Paint): 25%
TBT (Total Blocking Time): 30%
The other small percentages come from smaller metrics, but these three are the main ones.
The reason CLS stands out is simple: it’s usually the easiest one to fix.
Why CLS is easier to fix than LCP or TBT
LCP and TBT are often tied to how apps and scripts load on your site. On Shopify, every app adds its own JavaScript files, which pile up quickly. Even removing or deferring them requires careful work so nothing breaks.
LCP measures how long it takes for the largest visible part of your page (like a hero image or heading) to fully load. That delay is often outside your control because it’s tied to how scripts from Shopify apps or third-party tools load.
TBT measures how long the main thread of your browser is “blocked” from responding. That’s also script-related and usually requires deeper optimization.
CLS, on the other hand, is about how stable your layout is while loading. It doesn’t depend much on app scripts. Even when it does, it's easy to find and correct.
Here’s the usual pattern:
An image or banner doesn’t have defined height or width.
The browser loads the text first, then pulls in the image later.
The image pushes everything down once it appears.
That’s your layout shift. And it’s often fixed by defining the right dimensions in CSS or Liquid.
How to find and fix high CLS on your Shopify store
You can see your CLS score in PageSpeed Insights or Lighthouse. Look for a line labeled “Cumulative Layout Shift.”
If your CLS is above 0.1, you’re in the range where users might notice shifting. Above 0.25 means it’s definitely worth fixing.
The process usually looks like this:
Run a test in PSI or Chrome DevTools. Note which elements are shifting during load. PSI highlights them.
Locate the element in your theme code. It could be a slideshow, banner image, or app embed.
Set fixed dimensions. Add height and width values directly in your CSS or Liquid file.
Retest. The improvement should show up immediately after publishing.
In many cases, this takes less than an hour.
Note: this is just the simplest case. It doesn't mean that it's always possible to just add a width and a height value. Sometimes, the element can't be easily targeted, the width and height isn't a fixed number, etc.
Why better CLS improves more than just the score
A smoother layout helps with more than metrics. It directly affects how users and Google see your site.
Here’s what happens when you fix it:
Better UX. Visitors can interact with your page without sudden movement or broken clicks.
Better SEO. Google includes Core Web Vitals in ranking signals, so higher CLS scores can nudge your site up.
Better ad performance. Google Ads evaluates landing page experience, and CLS is part of that score.
Even small drops make a difference. For example, going from 0.2 to 0.02 can raise your PSI score by around 10 points.
Quick FAQ
1. What’s a “good” CLS score for Shopify stores? Anything below 0.1 is considered decent. Below 0.05 is excellent and rarely noticeable to users. You should be able to achieve excellent.
2. Can theme updates or app installs increase CLS again? Yes. Some theme updates overwrite your CSS, and new apps might add shifting widgets. Always retest after changes.
3. Does CLS affect mobile more than desktop? Usually, yes. Mobile networks load elements in smaller chunks, so shifts are more visible.
4. Can page builders like PageFly or GemPages cause high CLS? They can, especially if dynamic blocks or animations resize as they load.
5. Should I fix CLS before LCP or TBT? If your CLS is high, start there. It’s the easiest fix and gives fast results.
Wrapping up
If your Shopify performance score feels stuck, start with CLS. It’s measurable, fixable, and impacts multiple parts of your site at once. Most stores can improve it without touching complex scripts or removing apps.
Once the layout is stable, you can move on to bigger challenges like LCP and TBT - but for now, fixing CLS might be the quickest win your store needs.
