Core Web Vitals explained for business owners

If you've ever run your website through a Google tool, or read a report from a web designer, you may have come across the term “Core Web Vitals”, along with letters like LCP, INP and CLS. It sounds like something only developers need to worry about.

But the idea behind it is simple, and it's about your customers. Core Web Vitals are Google's way of measuring how a page feels to the people using it. This post explains each one without jargon. For the wider set of scores, see what is Google Lighthouse.

The three questions

Imagine a customer tapping a link to your website. Core Web Vitals answer three questions about their experience:

1. How quickly did the main content appear?
2. When they tapped something, how quickly did the page respond?
3. Did things jump around while the page was loading?

Each has a name and a measure.

1. Largest Contentful Paint (LCP): how fast it loads

LCP measures how long it takes for the biggest thing on the screen, usually the main photo or heading, to appear. It's the moment a visitor feels “the page is here”.

• Good: within 2.5 seconds
• Needs improvement: between 2.5 and 4 seconds
• Poor: more than 4 seconds

What usually slows it down

• A huge hero photo that hasn't been compressed. See WebP and AVIF.
• Slow hosting, or a server far from the visitor. See what is a CDN.
• Lots of code that has to load before anything appears

2. Interaction to Next Paint (INP): how quickly it responds

INP measures how quickly the page reacts when someone taps a button, opens a menu or types in a form. A good page responds almost instantly. A poor one makes people tap twice, wondering whether anything happened.

• Good: within 200 milliseconds (a fifth of a second)
• Needs improvement: between 200 and 500 milliseconds
• Poor: more than 500 milliseconds

What usually slows it down

• Heavy scripts running in the background, such as chat widgets, pop-ups and trackers
• Too many plugins, each adding its own code

3. Cumulative Layout Shift (CLS): how steady it stays

CLS measures how much things move around while the page loads. You've probably experienced this: you go to tap a button, an image loads above it, the button jumps down and you tap something else by mistake.

• Good: a score of 0.1 or less
• Needs improvement: between 0.1 and 0.25
• Poor: more than 0.25

What usually causes it

• Images without a reserved space, which push content down as they load
• Banners, pop-ups or adverts that appear above existing content
• Fonts that load late and change the size of text

How they're measured

Core Web Vitals are measured in two ways:

• From real visitors (field data). If enough people with the Chrome browser visit your site, Google collects anonymous measurements of their real experience. This is what Google uses when it considers page experience.
• In a test (lab data). Tools like Lighthouse load your page in a simulated phone or computer and estimate the scores. This is useful for spotting problems, even on a small site with few visitors.

A small local business website often doesn't have enough visits for field data, so lab tests are the main guide. See how to test your own website with PageSpeed Insights.

Why they matter for a small business

Customers feel them

A slow, jumpy, unresponsive page is frustrating, especially on a phone with mobile data. Frustrated visitors leave. See how a slow website quietly loses customers.

Google considers them

Google has said that page experience, including Core Web Vitals, is one of many things it considers when ranking pages. Good content and relevance matter more, but when other things are equal, a better experience helps. It's part of technical SEO.

They reflect care

A site that scores well has usually been built carefully: compressed images, clean code, no unnecessary extras. That care shows in how it feels to use.

What you can ask your web designer

1. Are images compressed and sized for each screen?
2. Do images and banners have space reserved, so nothing jumps?
3. Can we remove scripts and plugins we don't really need?
4. Is the hosting fast, with a CDN?
5. What are our Core Web Vitals on mobile?

How we build

Every site we build is tuned to score 90+ on Google's Lighthouse for performance, SEO, accessibility and best practices, which includes paying close attention to all three Core Web Vitals. We prepare pages in advance with Next.js, compress images into modern formats, reserve space for every image and keep extra scripts to a minimum. See how we build, including real scores from our client sites.