Core Web Vitals in plain language: LCP, INP and CLS

“Your Core Web Vitals need improvement.” If you have ever opened Google Search Console, you have probably seen a line like that. Behind the acronyms are three simple questions about how your page feels to a visitor.

LCP: how fast does the main content appear?

Largest Contentful Paint is the moment the biggest thing on the screen, usually the hero picture or the main heading, has finished showing. It is the moment a visitor thinks “the page is here”.

• Good: 2.5 seconds or less
• Needs improvement: up to 4 seconds
• Poor: more than 4 seconds

Usual fixes: a hero picture that is far too large, a slow server, or a page that waits for fonts and scripts before showing anything. Serve the hero picture in a modern format at the size it is shown, and don’t lazy-load the one picture everybody sees first.

INP: how quickly does the page react?

Interaction to Next Paint measures the delay between a tap or a click and the moment the screen visibly responds. It replaced the older FID measure in March 2024, because FID only looked at the very first interaction. INP looks at all of them.

• Good: 200 milliseconds or less
• Needs improvement: up to 500 milliseconds
• Poor: more than 500 milliseconds

Usual fixes: too much JavaScript running at once. Every tracking script, chat widget and slider competes for the same moment. Remove what you don’t need, load the rest later, and keep heavy work away from the moment someone taps.

CLS: does the page jump around?

Cumulative Layout Shift measures how much the content moves while you are looking at it. You know the feeling: you go to tap a link and an advert pushes it down, so you tap the wrong thing. CLS is a score without a unit.

• Good: 0.1 or less
• Needs improvement: up to 0.25
• Poor: more than 0.25

Usual fixes: pictures and videos without a width and height in the HTML, banners that slide in at the top, and web fonts that swap in with a different size. Reserve the space before the content arrives.

Lab numbers and field numbers

There are two kinds of numbers. Lab numbers come from a test run, like a scan: one device, one connection, repeatable. Field numbers come from real visitors over the last 28 days, and Google looks at the 75th percentile: three out of four visits must be good for the page to pass. A page can do well in the lab and still fail in the field when your visitors use older phones or slower connections.

Do they affect search rankings?

Yes, but modestly. Google uses them as one signal among many, and great content on a slow page can still rank. The bigger reason to care is your visitors: slow, laggy or jumpy pages lose people, whatever their ranking.

Where to find yours

The Speed gauge in every DesignScan report shows how your page loads on a phone and a desktop, and the UX Doctor names the heavy pictures and scripts behind a slow result. Scan your site to see where you stand.