Core Web Vitals: what the three numbers mean

What they are

Core Web Vitals are three measurements of how a page feels to a visitor: how fast the main content appears, how fast the page answers a tap, and whether things jump around while loading.

The three numbers

Largest Contentful Paint (LCP) is how long until the biggest thing on the screen has loaded. Interaction to Next Paint (INP) is how fast the page reacts after a tap or click. Cumulative Layout Shift (CLS) is how much the page moves while it loads.

Google's guidance for a good result: LCP within 2.5 seconds, INP of 200 milliseconds or less, CLS of 0.1 or less, measured at the 75th percentile of page loads, which means three out of four visits do at least that well.

Two kinds of numbers

Lab numbers come from one simulated load on one device with fixed network conditions. They help find problems, and they can miss what real visitors feel. Real-visitor numbers come from actual visits over the previous 28 days.

Lab numbers move a little from run to run. The lab tool's own documentation says the median of five runs is twice as stable as one run. So treat one reading as one reading.

What we check

On your home page we read the lab test of the page on a phone, and the real-visitor numbers when Google has them. We say what we saw on the date we read it.

Ask your web developer

Which element is the largest on the first screen, and how big is its file? Do images and ads have a fixed size so nothing jumps? Which scripts run when a visitor taps?

What we do not say

A number near the edge of a band can land on either side on the next reading. We do not promise that a change will move your ranking.