Core Web Vitals sounds like a technical checklist, but it's really three plain questions about what it feels like to use your site: how long before something shows up, how fast it responds when tapped, and whether it jumps around while loading. Google publishes exact thresholds for "good" on all three, and they're worth knowing without the jargon.
The three metrics, translated
Largest Contentful Paint (LCP) asks: how long until the biggest, most important thing on the page actually appears? Google's threshold for "good" is 2.5 seconds or less. In plain terms, this is the wait between tapping a link and seeing the thing you came for, whether that's a headline, a photo, or the main block of the page.
Interaction to Next Paint (INP) asks: when someone taps a button or a link, how long until the page visibly responds? Google's threshold is 200 milliseconds or less. This is the difference between a page that feels instant when you tap it and one that feels like it's thinking about it.
Cumulative Layout Shift (CLS) asks: does stuff move around while the page is loading? Google's threshold is 0.1 or less, on a scale where 0 means nothing shifted at all. This is the metric behind the frustrating moment when you go to tap a button and the page jumps at the last second, so you tap an ad instead.
The detail that matters: it's measured at the 75th percentile
Google doesn't grade these on your best load, or your average load. Its own guidance specifies measuring "the 75th percentile of page loads, segmented across mobile and desktop devices." In practice, that means your site has to meet the threshold for at least three out of every four visits, not just the good ones on a fast connection in perfect conditions. A site that's fast on office wifi but slow on a customer's phone in a basement is failing this measurement even if it feels fine to you when you check it.
Why this is worth checking at all
A slow or jumpy page costs you visitors before they ever get to read what you wrote or see your phone number. See 9 signs your website is costing you customers for how that plays out in practice, and click-to-call: why your phone number belongs in the header for one specific way a slow or shifting page costs you a call directly, if a visitor taps the wrong thing because the layout moved.
How to actually check your own numbers
Two free tools do this without needing anything installed:
- PageSpeed Insights gives you a one-time check of a specific page, on both mobile and desktop, with the three scores above and specific suggestions for what's slowing it down.
- Search Console's Core Web Vitals report tracks these numbers across your whole site over time, based on real visitor data rather than a single test, which is the more honest long-term picture since it reflects actual customers on actual connections.
What usually causes each problem, in plain terms
- Slow LCP: often large, uncompressed images, or a server that takes too long to respond in the first place
- Slow INP: usually too much happening in the background (scripts, trackers, animations) competing for the browser's attention when someone taps something
- High CLS: images or ads that don't reserve their space in advance, so content shifts down once they finish loading
Questions
Do Core Web Vitals affect my Google ranking directly?
They're one signal among many, not the dominant one. A slow, jumpy site can still rank, but it's working against itself on every visit regardless of ranking, since it's losing real visitors the moment they arrive.
How do I know if my site is failing right now?
Run your homepage and one or two service pages through PageSpeed Insights. It's free and takes under a minute per page.
Is a perfect score necessary?
No. Meeting the "good" threshold at the 75th percentile is the actual bar Google sets, not a perfect number on every single load.