Core Web Vitals in plain English
6 min read · Updated
Core Web Vitals are three measurements Google uses to judge how a page feels to a real visitor. They sound technical, but each one answers a simple question a customer would ask: does it load, does it respond, and does it stay still?
Largest Contentful Paint: does it load?
Largest Contentful Paint (LCP) measures how long it takes for the biggest thing on the screen, usually your hero image or main heading, to appear. It’s the closest single number to “how long did I wait?”
- Good: 2.5 seconds or less
- Needs work: 2.5 to 4 seconds
- Poor: more than 4 seconds
This is the number behind “Mobile load time” in your report. The most common causes of a slow LCP are a huge hero image, slow hosting, and scripts that have to load before anything shows.
The fixes, in the order they usually help most:
- Compress and resize your hero image. This alone often cuts seconds.
- Stop scripts and styles from blocking the first paint.
- Speed up your server response with caching or better hosting.
Interaction to Next Paint: does it respond?
Interaction to Next Paint (INP) measures how quickly the page reacts when someone taps a button, opens a menu or types in a form. A page can look loaded but still feel frozen, because the browser is busy running code in the background.
- Good: 200 milliseconds or less
- Needs work: 200 to 500 milliseconds
- Poor: more than 500 milliseconds
Slow responses usually come from too much JavaScript: chat widgets, tracking tools, sliders and page-builder effects all compete for the phone’s attention. Removing plugins you don’t use is the easiest win.
Cumulative Layout Shift: does it stay still?
Cumulative Layout Shift (CLS) measures how much things jump around while the page loads. You know the feeling: you go to tap a button, an image loads above it, everything shifts down, and you tap an ad instead.
- Good: 0.1 or less
- Needs work: 0.1 to 0.25
- Poor: more than 0.25
It’s a score, not a time. The usual causes are images without a set size, ads or embeds that load late, and fonts that swap in and change the size of text. The fix is usually to give images and embeds a fixed width and height so the browser saves space for them.
Why these three?
Google chose these because they line up with what actually frustrates people. Waiting, tapping and nothing happening, and things moving under your thumb are the three things that make people leave a page. A site that does well on all three feels quick and solid, even if it isn’t the fastest on paper.
Do small businesses really need to care?
You don’t need perfect scores. You do need a site that doesn’t lose customers. For most small business sites:
- LCP is the one to watch. It’s usually the weakest, and it’s where the biggest gains are.
- CLS is usually a quick fix once someone knows where the jumping comes from.
- INP tends to be fine on simple sites and only becomes a problem when a site has piled up plugins.
If your report shows these as Good, you can stop worrying about speed and spend your time on other areas. If they’re Needs work or Poor, fixing them helps visitors straight away and can nudge your Google rankings too.
Where to go from here
Run a free scan to see your numbers. Your report translates them into plain English and lists the fixes in order of impact. Then read why is my website slow? for the most common causes, or image optimisation for non-designers for the single biggest quick win. You can also learn more about our speed audit.
Want the full picture? See what our free speed audit checks
Common questions
Do Core Web Vitals affect my Google ranking?
They're one of many signals Google uses. Good content still matters more, but between two similar pages, the faster and more stable one has an edge. They matter even more for how visitors experience your site.
Why does my score change every time I test?
Lab tests simulate a phone and a network, and small differences in timing change the result each run. Look at the trend over a few tests rather than a single number.
What's the difference between lab data and field data?
Lab data comes from a simulated test, which is what a scan runs. Field data comes from real Chrome users visiting your site over the past month. Google only has field data for sites with enough traffic.