Speed Core Web Vitals explained for business owners: LCP, INP and CLS

If you’ve ever received a speed report full of acronyms, this guide is for you. It explains what each metric measures, what good looks like, how to check them without being technical and why they matter for your business, not just for Google.

The three metrics, in plain English

Metric	What it measures	Good	Needs improvement	Poor
LCP: Largest Contentful Paint	How long the main content (the largest image or text block) takes to appear	2.5 s or less	Up to 4 s	Over 4 s
INP: Interaction to Next Paint	How long the page takes to respond when you tap a button, open a menu or type	200 ms or less	Up to 500 ms	Over 500 ms
CLS: Cumulative Layout Shift	How much things move around while loading (the button that jumps just as you go to tap it)	0.1 or less	Up to 0.25	Over 0.25

A page “passes” when at least 75% of visits get good values, measured separately on mobile and desktop. INP replaced the earlier metric, FID, in March 2024, because it measures responsiveness throughout the visit, not just on the first tap.

Lab data vs. field data

There are two kinds of measurement, and it helps not to mix them up:

• Field data: what your real visitors experience on their devices and connections. It’s what Google uses, and it appears in Search Console and PageSpeed Insights when there’s enough traffic.
• Lab data: a simulation under fixed conditions, such as the Lighthouse score. It’s useful for finding problems and comparing before and after, but it isn’t the real experience.

If your site doesn’t get much traffic, there may be no field data. In that case, lab data is your best reference, as long as you treat it as an estimate.

How to check them yourself

1. Open PageSpeed Insights, Google’s free tool, and enter your home page address.
2. Look at the top section first, with real visitor data, if there is any. Check the mobile tab: it’s usually the toughest.
3. Repeat with your two or three most important pages, such as a service page or your contact page.
4. In Search Console, open the Core Web Vitals report to see all your pages grouped.
5. Save the numbers with the date. You’ll use them to compare after any change.

Why they matter for your business

Google includes these metrics among its page experience signals, but they aren’t the only thing that decides your ranking: a highly relevant page can rank even if it isn’t the fastest. The deeper reason is simpler: a page that’s slow to show up or doesn’t respond makes people leave before they read your offer, especially on mobile.

That’s why it’s worth looking at these metrics alongside what happens on your site: whether requests come in, whether the form works and which devices people use.

What usually hurts each metric

High LCP

Very heavy hero images, a server that’s slow to respond, fonts or scripts that block loading, or a main image that’s lazy-loaded when it should load first.

High INP

Too much JavaScript: plugins, page builders, chat widgets, maps and tracking tools that keep the browser busy when someone tries to use the page.

High CLS

Images without set dimensions, banners or notices injected above the content, and fonts that change size as they load.

Where to start

Measure, fix what weighs most and measure again. On WordPress, the most common causes are images, plugins and the server; we go through them step by step in our guide on why your WordPress site is slow.

Frequently asked questions

Do I need a 100 PageSpeed score?

No. The lab score is a guide. What matters is real-visitor data and a page that works well for your clients.

Why do results change every time I test?

Lab measurements vary with the network and server load at that moment. Test several times and compare trends.

Is FID still a thing?

Not as a core metric. INP replaced it in March 2024.