This ultimate guide to Core Web Vitals explains what they are, why they matter for both SEO and user experience, and how to measure and improve them using practical, real-world tactics.
If you’ve ever wondered “What exactly are Core Web Vitals, why are they such a big deal, and how the heck do we actually improve them?” this guide is for you.
Get comfy, grab a drink and prepare to discover everything there is to know about Core Web Vitals. If you still have questions after reading, do not hesitate to get in touch with me (my details are below).
Core Web Vitals are Google's way of measuring whether your website delivers a smooth, speedy, and visually stable experience. Think of them as your site's fitness score.
And yes, this matters. A lot.
If you want higher conversions, better rankings, and happier visitors, you need to get your Web Vitals in order.
Here’s what Core Web Vitals actually measure.
Measures loading speed
Target: 2.5 seconds or faster
What it tracks: The time it takes for the largest visible element (usually a hero image or heading) to load. It reflects how fast users feel the page is loading.
Common causes of slow LCP:
Render-blocking JavaScript or CSS
When your browser loads a web page, it reads the HTML from top to bottom. If it hits a big chunk of JavaScript or CSS in the <head> that hasn't been told to load "later," it stops everything and waits until it’s finished loading and processing those files.
In simple terms, it’s like saying, “Hold on, I need to read all these instructions before I can show anything.”
The biggest piece of content (like a banner or heading) gets delayed while the browser loads scripts that might not even be needed right away.
How to fix it:
Content Delivery Networks
A CDN stores copies of your site’s assets, images, scripts and stylesheets, on servers around the world. When someone visits your site, the content gets delivered from the location closest to them.
Why it’s a problem:
If you’re not using a CDN, your content may have to travel a long way to reach the visitor’s browser. That slows everything down, especially for users outside your primary hosting region.
How to fix it:
Use a CDN like Cloudflare, Bunny, or Fastly to serve static assets faster and reduce latency.
Measures responsiveness
Target: 200 milliseconds or less
What it tracks: The time between a user interaction and the next visible change on the page. This includes clicking, tapping, and typing.
Common causes of poor INP:
When your browser is busy crunching code (parsing, compiling, executing), it can’t respond to the user until it finishes what it’s doing. This is called blocking the main thread.
A long task is any task that takes more than 50 milliseconds. When your site has a few of these chained together, it creates a laggy, unresponsive experience.
For example, on an eCommerce site, if the browser is too busy doing other things, it can’t respond to you clicking the "Add to basket" button.
How it happens:
Event handlers are the functions triggered when someone interacts with your site - like clicking, tapping, or typing.
If they’re written poorly or are doing more work than needed, they slow everything down.
Examples include:
Bottom line: Your site should feel responsive to every interaction. If it’s pausing to "think" too often, that’s likely due to inefficient handling under the hood.
Measures visual stability
Target: 0.1 or lower (When we say a CLS score should be 0.1 or lower, we're referring to a unitless score calculated by Google based on layout instability.)
What it tracks: Whether elements on the page shift unexpectedly while loading. Ever click the wrong button because it jumped out of the way? That.
Common causes of bad CLS:
Google used to rely on First Input Delay (FID) to measure responsiveness, but FID had a major flaw. It only measured the delay of the first interaction.
INP is a much better measure. It tracks all interactions across the entire session and focuses on the worst-performing one. It reflects the real user experience far more accurately.
As of March 2024, INP has officially replaced FID as a Core Web Vital. If you’re still reporting on FID, it’s time to move on.
Core Web Vitals are part of Google’s Page Experience signal. This includes:
Improving these won’t suddenly put you at the top of page one, but falling short can definitely hold you back. Google uses real user data from Chrome, so these scores are based on what people actually experience on your site.
When content quality is equal, page experience becomes the tie-breaker.
There’s a common misconception that Web Vitals are just for SEO. They’re not. They’re for people.
Google uses them because they reflect what users care about.
This is where SEO and UX meet. If your site performs well, everyone benefits.
You can’t fix what you don’t measure. Fortunately, there are plenty of tools that help you diagnose and track Core Web Vitals.
We appreciate that the following information is all very technical, if you would like to discuss these elements further, do not hesitate to reach out to us.
If your site feels slow or unstable, it probably is. Run a test or get in touch and we’ll take a look.
Our Digital Marketing and Support teams work collaboratively to make sure your site has optimised core web vitals. We realise that as sites change, your CWV score can change, that’s why we do 6 monthly or quarterly reviews to make sure your site always scores well.
We monitor before and after results in Search Console, Lighthouse, and Pingdom. You'll see exactly what changed and why it matters.
People trust fast websites. It’s as simple as that.
When a site loads quickly, feels stable, and reacts instantly, it reflects on your brand. You look credible. Professional. Worth the click.
Fixing Core Web Vitals isn't just about SEO. It's about delivering a better experience to the people who visit your site and trust you with their time, their attention, and their money.
Do Core Web Vitals affect desktop and mobile rankings?
Yes. Google scores them separately. Your desktop site might pass, while mobile fails.
How long before changes are reflected in rankings?
Typically a few weeks. Field data is based on a 28-day rolling average.
Can you optimise my WordPress or Shopify site?
Yes. We’ve worked across Drupal, WordPress, Shopify, Umbraco, Craft, and custom builds. There's almost always room for improvement.
Is it worth the effort?
Absolutely. Improved Vitals often correlate with better rankings, lower bounce rates, and increased conversions. It's one of the most measurable upgrades you can make.
If you’ve read this far and you're still with me, thank you. Hopefully you now know what Core Web Vitals are, why they matter, and what to do next.
If you’d like a second pair of eyes on your site or a full audit, feel free to drop me a line.
richard.hunter@m-w.co.uk
01722 335105 (Salisbury office)
Or pop in to see us in Covent Garden or Old Sarum
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This article was written by Richard Hunter, Head of Digital Marketing at Moore-Wilson.
If you would like to talk to Richard about your Digital Marketing, do not hesitate to contact us.
Last edited on 17/09/2025
