Core Web Vitals are three measurements Google uses to judge how pleasant a page is to use: how quickly the main content appears (LCP), how quickly it responds to a tap (INP), and how much it jumps around while loading (CLS). A page that fails these ranks below an otherwise equal page that passes — and most sites built on templates and cheap hosting fail.
Three numbers, no jargon
LCP — Largest Contentful Paint. How many seconds pass before the biggest thing on screen appears, usually the main photo or headline. Threshold: up to 2.5 seconds is good, over 4 is poor.
INP — Interaction to Next Paint. When a visitor taps something, how long the page "thinks" before anything happens. Threshold: up to 200 milliseconds is good. This replaced the older measure (FID) in 2024 and is stricter.
CLS — Cumulative Layout Shift. How much the content jumps as it loads — that moment when you go to tap a button and it moves because an image loaded above it. Threshold: up to 0.1 is good.
Google measures this on real visitors, on real phones, on real networks. Not on your office laptop.
Why this matters even if you are not a developer
Two reasons, both financial.
First: Google uses this as a ranking signal. Between two pages with similar content, the faster one goes higher. It does not decide everything — but it is the one ranking factor you can directly measure and fix.
Second, and more important: people do not wait. A page that takes five seconds to load on a phone loses a meaningful share of visitors before they see anything. Those are enquiries you did not get, and never knew you lost.
Why most sites fail
From what I see when clients arrive with an old site, it is almost always the same set of problems:
- Huge images. A 4 MB photo dropped straight from a phone where 80 KB would do. This is the number-one cause and the easiest to fix.
- Page builders and too many plugins. WordPress with Elementor and twenty plugins loads megabytes of code before showing anything.
- Cheap shared hosting. A server that answers slowly cannot be optimised from the page side.
- Third-party scripts. Chat widgets, tracking tools, fonts from external servers — each one adds waiting.
- Nothing is reserved. Images without defined dimensions, so content jumps as they load.
How to check your site in a minute
Open PageSpeed Insights, paste your address, and look at the section "Discover what your real users are experiencing" — those are real numbers, not a lab test. If it says "Passed", you are fine. If not, the exact causes are listed below it.
Check the mobile view, not desktop. That is where most sites fail, and where most of your visitors are.
How I do it
The sites I build pass these measures because it is designed in from the start rather than patched afterwards: the page is generated in advance instead of assembled on every visit, images are automatically resized and served in a modern format, fonts live on the same server as the page, and there are no third-party scripts you did not ask for. That is the technical SEO I include in every site — not as an extra, but as the way the work is done.
Frequently asked
Can an old site be fixed to pass? Often yes, if the problem is only images and plugins. If the problem is the template itself or the hosting, a new site is usually cheaper than the repair. I look for free and tell you what is realistic.
How fast is "fast enough"? Green on all three measures in PageSpeed, for mobile. Anything beyond that is a bonus visitors feel, but Google no longer rewards.