Core Web Vitals: How to Measure and Improve Them

In short: Core Web Vitals are three Google metrics that now define how a website performs for real users, and in 2025 only 48% of websites passed them on mobile, according to the Web Almanac. Most gains come from a handful of simple fixes (images, third-party scripts, fonts), made in the order your real visitor data reveals.

Building a website has never been easier. Making it fast, stable and pleasant on a phone is another matter. This guide is for small business owners, retailers and professional firms who want to understand where their site stands and what to fix first, without being developers.

What does website performance mean?

The word covers two things. Technical performance: the site loads quickly, responds when you tap a button and does not jump around while loading. And business performance: the site turns visitors into leads or sales. The two are linked, because a visitor who waits, or who taps the wrong button after the layout shifts, is more likely to leave.

A study run by Deloitte and the research firm 55 for Google, published as “Milliseconds make millions”, measured that link on 37 European and American brands over 30 million sessions at the end of 2019. A 0.1 second improvement in mobile site speed came with an 8.4% rise in conversions for retail sites and 10.1% for travel sites. That is a correlation observed on those sites, in a study commissioned by Google: it shows a direction, not a promise for yours.

What are the three Core Web Vitals?

Google sums up the loading experience in three measures:

Metric	What it measures	“Good” threshold
LCP (Largest Contentful Paint)	Time to display the largest visible element	2.5 seconds or less
INP (Interaction to Next Paint)	Delay before the page reacts to a tap, click or keystroke	200 milliseconds or less
CLS (Cumulative Layout Shift)	Unexpected visual shifts while the page loads	0.1 or less

These thresholds are assessed at the 75th percentile of visits: three visitors out of four must get a good experience, measured separately on mobile and desktop. INP replaced the older FID metric in March 2024.

Google writes that it “highly recommends” achieving good Core Web Vitals for success with Search, and that page experience aligns with what its core ranking systems seek to reward. It is not the top ranking factor; relevance comes first. But between two equally relevant pages, and for conversion, the difference is real.

How do websites score today?

The Performance chapter of the Web Almanac 2025, published by HTTP Archive from data collected in July 2025, gives a snapshot of the web:

• 48% of sites pass all three Core Web Vitals on mobile, up from 44% in 2024 and 36% in 2023. On desktop, the figure is 56%.
• LCP is the weak spot: 62% of sites are “good” on mobile, against 77% for INP and 81% for CLS.
• The slowest element is almost always an image: that is the case on 76% of mobile pages.
• About 17% of mobile pages still lazy-load their main image, which delays precisely the display that LCP measures.

In other words, if your site is slow, the most likely culprit is a large image at the top of the page, poorly prepared or poorly loaded.

How do you measure your site’s Core Web Vitals?

Three free tools are enough:

1. PageSpeed Insights. Enter a page URL. The top section shows real data from Chrome users over the last 28 days when traffic is high enough; the bottom section is a lab test with a list of suggested fixes.
2. The Core Web Vitals report in Google Search Console. It groups your pages by problem (“LCP issue: longer than 2.5s on mobile”, for example). This is the report that tells you which pages to fix first.
3. Your analytics tool (Google Analytics 4 or similar). It shows landing pages, engagement rate and conversions, so you can tie technical issues to business results.

Our roundup of SEO tools explains how to set up Search Console if you have not done it yet.

A classic trap: the score out of 100 in the lab test changes from one run to the next and does not always match what real visitors experience. Trust field data first.

What should you fix first?

Here is the order that brings the most results for the least effort on a small business website, WordPress or otherwise.

1. Images

• Resize them to their real display size: a 4,000 pixel wide photo shown at 800 pixels wastes most of its weight.
• Use a modern format (WebP or AVIF).
• Do not lazy-load the image at the top of the page, which often determines LCP. Lazy loading is useful for images further down.
• Set width and height in the code so the browser reserves the space and avoids layout shifts (CLS).

2. Third-party scripts

Live chat, social media widgets, ad pixels, embedded maps, heavy cookie banners: each one adds code to run. Take an inventory, remove what you no longer use, and load the rest after the main content displays. This is often what improves INP.

3. Fonts

Stick to two families and a few weights, host them on your own server if possible, and preload the one used in the main heading.

4. Hosting and caching

Very cheap shared hosting can respond slowly from the first request. Turn on page caching, and compare your server response time before deciding to switch providers. Our guide to web hosting explains what to look for.

5. Plugins and page builders

On WordPress, every plugin can add its own files to every page. Deactivate the ones you do not use, and check that your page builder is not loading modules you never use.

Is performance only about speed?

No. A fast site that fails to persuade still underperforms. Three practices complete the technical work.

User testing. Ask three or four outside people to complete a specific task on your site, on their own phone: find your rates, book an appointment, request a quote. Watch without helping. Broken links, buttons nobody can find and forms that are too long show up within minutes.

Pages designed for one action. Every important page should lead to a clear next step. The principles of a good landing page apply to a service page too.

Content that stays current. A site whose information is years old loses visitors’ trust. A business blog updated regularly forces you to revisit the site and feeds your search visibility.

What does a typical fix look like?

Take a 15-page website for a CPA firm or a law office that shows a mobile LCP of 4.1 seconds in PageSpeed Insights. The diagnosis shows that the LCP element is the team photo at the top of the homepage, 2,400 pixels wide, lazy-loaded by the theme.

The fixes, in order: remove lazy loading from that image, resize it to its display width, convert it to WebP, then remove a reviews widget that loads an external script on every page. Half a day of work. Field data updates gradually since it covers the previous 28 days, so wait a month before judging the result.

Slowness is among the most common SEO mistakes precisely because it creeps in silently, one plugin at a time. A quarterly check in PageSpeed Insights is enough to catch it before it costs you visitors.