Core Web Vitals, Explained Without the Jargon
The three numbers Google uses to describe how a page feels to a real visitor.
Core Web Vitals are three numbers Google uses to describe how a page feels to a real visitor: how fast the main content shows up, how quickly the page reacts when you tap something, and whether things jump around while it loads. Google says it highly recommends good Core Web Vitals for success in Search. They won't rescue a weak page, but they're one of the few page-experience signals you can measure directly.
The short version
- LCP (loading) should be 2.5 seconds or less, INP (responsiveness) 200 milliseconds or less, and CLS (layout shift) 0.1 or less.
- Google judges these at the 75th percentile of real visits, so at least three out of four visits need to be "good".
- INP replaced First Input Delay (FID) in March 2024 and looks at every interaction, not just the first tap.
- Fix the server first, then the main image, then the scripts.
The three numbers and what "good" means
One detail trips people up: Google judges these at the 75th percentile of real visits. Basically, at least three out of every four visits need to hit "good" for the page to pass. A fast result on your own laptop and Wi-Fi doesn't count for much if most visitors are on older phones.
INP is the newest of the three. It replaced an older metric, First Input Delay (FID), in March 2024. FID only timed the first tap; INP looks at every interaction, which is why many sites that used to pass now don't.
| Metric | What it measures in plain English | Good | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | How long until the biggest thing on screen (usually the main image or headline) appears | 2.5 seconds or less | Over 4 seconds |
| INP (Interaction to Next Paint) | How long the page takes to visibly respond after you click, tap or type | 200 milliseconds or less | Over 500 milliseconds |
| CLS (Cumulative Layout Shift) | How much the page jumps around while it loads | 0.1 or less | Over 0.25 |
Why a page fails each one
Slow LCP usually comes from:
- A slow server. If the HTML takes a second to arrive, everything after it starts late. (The Server Speed & Page Weight Checker measures exactly this.)
- The main image is set to lazy-load. Lazy loading is great for images further down the page, but it delays the one image people see first.
- The main image is a CSS background or sits inside a slider script, so the browser finds it late.
Slow INP usually comes from too much JavaScript running at once: tag managers, chat widgets, pop-ups and heavy themes all compete for the same processing time your visitor's tap needs.
High CLS usually comes from:
- Images and videos without width and height, so the browser can't save space for them.
- Ads, cookie banners or embeds that push content down after it's already shown.
- Web fonts that are a different size from the fallback font the page first shows.
How to check your own pages
- Open PageSpeed Insights and enter a page address. The top section ("Discover what your real users are experiencing") is real visitor data. The lower section is a lab test, which is useful for finding causes but isn't what Google uses.
- In Google Search Console, open the Core Web Vitals report to see which groups of pages pass or fail across your whole site.
- Run the page through the Server Speed & Page Weight Checker to see whether the server itself is the bottleneck, and the Mobile Viewport Checker to confirm phones are set up correctly.
New or small sites often see "no data" in the real-visitor section. That's normal: Google only reports field data once a page gets enough Chrome visits. Use the lab results as a guide until then.
Start with the server
A slow server makes a good LCP very hard to reach. Check your server response time, HTML size and compression in one scan.
Server Speed & Page Weight Checker · free, no sign-up
The short version
Get the main content on screen within 2.5 seconds, respond to taps within 200 milliseconds, and keep layout shifts under 0.1, for at least three out of four visits. Fix the server first, then the main image, then the scripts.
Sources
I checked the facts in this guide against these pages (last reviewed November 6, 2026).
Try it on your own site
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