What Are Core Web Vitals And How To Improve Them

If you have spent any time researching SEO over the last few years, you will have come across the term Core Web Vitals. Google introduced them as a ranking signal, and yet a surprising number of website owners either do not fully understand what they are or have done very little to address them. If your site is slow, clunky, or frustrating to use on a mobile device, there is a very real chance that your Core Web Vitals are working against you, both in terms of user experience and your ability to rank well in search results. Understanding what Core Web Vitals are and how to improve them is no longer optional if you are serious about your website's performance.

What Are Core Web Vitals?

Core Web Vitals are a set of specific metrics that Google uses to measure the real-world experience of users visiting your website. They focus on three key areas: loading performance, interactivity, and visual stability. Each of these is given a measurable score, and Google uses those scores as part of its Page Experience ranking signals.

The three metrics that make up Core Web Vitals are Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). It is worth noting that INP replaced First Input Delay (FID) as an official Core Web Vital in March 2024, so if you are reading older guides that still reference FID, they are out of date. Each of these metrics tells Google something specific and important about how your site performs for actual visitors.

Largest Contentful Paint (LCP)

LCP measures how long it takes for the largest visible piece of content on your page to load. This could be a hero image, a large block of text, or a video thumbnail. Google considers anything under 2.5 seconds to be a good score. Between 2.5 and 4 seconds needs improvement, and anything above 4 seconds is considered poor.

The reason LCP matters so much is that it represents the perceived loading speed of your page. A visitor does not care about your server response time in technical terms; they care about how quickly they can see something meaningful on the screen. If your page feels slow, they will leave, and Google knows this.

Common causes of a poor LCP score include slow server response times, render-blocking JavaScript and CSS, unoptimised images, and third-party scripts that are loading before your main content. Addressing your image sizes is often the most impactful starting point. Tools like Squoosh allow you to compress images without destroying quality, and switching to modern formats like WebP can make a significant difference to how quickly your pages load.

Where to start: Run your site through Google PageSpeed Insights and look specifically at what element is flagged as your LCP element. Once you know what it is, you can focus your efforts on optimising that specific asset rather than trying to fix everything at once.

Interaction to Next Paint (INP)

INP measures the responsiveness of your page to user interactions. When someone clicks a button, taps a link, or interacts with a form, INP captures how long it takes for the browser to respond visually to that interaction. A good INP score is under 200 milliseconds. Anything between 200 and 500 milliseconds needs improvement, and above 500 milliseconds is considered poor.

This metric replaced FID because it gives a more complete picture of interactivity throughout the entire page visit, rather than just measuring the very first interaction. A page might respond well to the first click but become sluggish as more scripts load in the background. INP captures that broader experience.

Heavy JavaScript is typically the biggest culprit when it comes to poor INP scores. If your site relies on large JavaScript bundles, complex third-party widgets, or bloated page builders, your browser's main thread can become overloaded, making it slow to respond to user inputs. Reducing unused JavaScript, deferring non-critical scripts, and breaking up long tasks are all strategies that can bring your INP score down to an acceptable level.

Where to start: Use the Web Vitals Chrome Extension to measure your INP score in real time as you interact with your own pages. It gives you an immediate sense of where the friction points are.

Cumulative Layout Shift (CLS)

CLS measures visual stability. In simple terms, it tracks how much your page layout shifts around while it is loading. If you have ever been reading an article and suddenly the text jumps down because an image or advertisement loaded above it, that is a layout shift. A good CLS score is 0.1 or below. Between 0.1 and 0.25 needs improvement, and anything above 0.25 is poor.

Layout shifts are genuinely frustrating for users, particularly on mobile devices where the screen is smaller and a sudden shift can cause someone to tap the wrong button or lose their place on the page entirely. It erodes trust and damages the overall impression of your site, regardless of how good your content actually is.

The most common causes of poor CLS include images and videos without defined width and height attributes, dynamically injected content such as banners or cookie notices that push existing content down, and web fonts that cause a visible flash of unstyled text before loading. Defining explicit dimensions for all media elements is one of the most straightforward fixes available to most website owners.

Where to start: In Google Search Console, navigate to the Core Web Vitals report under the Experience section. This will show you which URLs on your site are flagged as having poor or needing improvement CLS scores, giving you a prioritised list of pages to address first.

How to Measure and Monitor Your Core Web Vitals

Understanding what Core Web Vitals are and how to improve them means very little if you are not regularly measuring where your site currently stands. Google provides several tools to help with this. Google Search Console gives you field data, which is real-world data collected from actual users visiting your site via Chrome. This is the data that Google itself uses when evaluating your site for ranking purposes.

PageSpeed Insights combines both field data and lab data, giving you a thorough picture of your performance alongside specific recommendations. Lighthouse, which is built into Chrome DevTools, is another excellent option for running detailed audits in a controlled environment.

It is important to understand the difference between field data and lab data. Lab data is collected in a controlled simulation and is useful for diagnosing issues, but field data reflects the genuine experience of your real visitors across a range of devices and connection speeds. Both have their place, but field data is what ultimately counts for ranking purposes.

Practical Steps to Improve Your Core Web Vitals

Improving your Core Web Vitals does not always require a full website rebuild. There are practical steps that most site owners can take without needing to become a developer overnight. Optimising and compressing images, implementing lazy loading for below-the-fold content, enabling browser caching, using a content delivery network (CDN) to serve assets closer to your users, and minimising render-blocking resources are all changes that can meaningfully move your scores in the right direction.

If you are using WordPress, plugins like WP Rocket can handle a significant portion of the technical heavy lifting, from caching and file minification through to lazy loading and database optimisation. Choosing a fast, well-coded theme also makes a considerable difference from the outset, as does selecting a hosting provider that prioritises server performance rather than simply offering the cheapest price point.

For sites built on other platforms, the principles remain the same. Reduce what you do not need, optimise what you do need, and ensure that what loads first is always what matters most to the user.

Core Web Vitals as Part of a Broader SEO Strategy

It would be a mistake to treat Core Web Vitals as a standalone task that you tick off and forget about. They are a living, evolving part of your site's health, and they sit within a much broader set of page experience signals that Google continues to develop. A site that loads quickly, responds well to interactions, and remains visually stable is a site that respects its visitors, and Google rewards that respect.

If you have not yet looked at your Core Web Vitals in any meaningful way, now is the right time to start. Log into Google Search Console, review your Core Web Vitals report, identify which pages are underperforming, and begin working through the issues in order of priority. It is a process, not a single task, but the cumulative effect of getting these metrics right is a faster, more trustworthy, and more competitive website.