Core Web Vitals Explained in Plain English

Core Web Vitals are a set of measurements from Google that describe how real people experience your pages. They focus on three things: how fast the main content loads, how quickly the page responds when someone interacts, and how stable the layout is while loading. They are part of Google's page experience signals.

The three metrics

LCP: Largest Contentful Paint

LCP measures how long it takes for the largest visible element, often a hero image or a big heading, to appear. A good LCP is 2.5 seconds or less, measured at the 75th percentile of visits.

To improve it:

• Compress and properly size your main image. See how to compress images.
• Do not lazy load the main top-of-page image.
• Use fast hosting and consider a CDN.
• Reduce render-blocking CSS and scripts.

INP: Interaction to Next Paint

INP measures how quickly the page responds when users click, tap, or type, looking at the interactions across the whole visit. It replaced the older First Input Delay metric in March 2024. A good INP is 200 milliseconds or less.

To improve it:

• Reduce and defer heavy JavaScript.
• Remove unneeded third-party scripts such as chat widgets and trackers.
• Break up long tasks so the browser stays responsive.

CLS: Cumulative Layout Shift

CLS measures unexpected movement of content while the page loads, like a button jumping just as you tap it. A good CLS is 0.1 or less.

To improve it:

• Set width and height on images and videos so space is reserved.
• Reserve room for ads, banners, and embeds.
• Avoid inserting content above existing content after load.
• Load fonts carefully. See web fonts without slowing your site.

Field data versus lab data

Field data comes from real visitors and is what Google uses for assessment. Lab data comes from simulated tests, which is helpful for debugging. They can differ. Learn how to use both in how to test website speed.

Where to see your scores

Google Search Console has a Core Web Vitals report for sites with enough traffic, and PageSpeed Insights shows both field and lab data for individual pages.

How much do they matter?

They are one set of signals among many. Strong content and relevance matter more, but good vitals improve the experience for every visitor. See why website speed matters.

Do not obsess

Thresholds can change, so check Google's documentation periodically. Concentrate on making pages genuinely quick and stable.

The bottom line

Aim for LCP of 2.5 seconds or less, INP of 200 milliseconds or less, and CLS of 0.1 or less. Fix the largest problems first and test again.