Core Web Vitals, Explained Without the Jargon
If you have ever run your site through a speed test, you have met Core Web Vitals: a small set of measurements Google uses to judge how a page feels to a real person. They are genuinely useful. They are also named as though they were designed to keep people out.
Here is what each one means, without the acronym soup.
LCP — how long until the page looks ready
Largest Contentful Paint measures how long it takes for the biggest thing on screen — usually your main heading or hero image — to appear. It is the closest thing to answering “how long does this page take to load?” as a human would judge it.
Aim for: under 2.5 seconds. Over 4 seconds is a problem worth fixing this month.
CLS — whether the page jumps around
Cumulative Layout Shift measures how much things move while the page is loading. You have felt this one: you go to tap a link, an image loads above it, everything shuffles down, and you tap an advert instead. Infuriating on a desktop, genuinely maddening on a phone.
Aim for: under 0.1. The usual cause is images and embeds that do not reserve their space before they arrive.
INP — how quickly the page answers you
Interaction to Next Paint measures the delay between you doing something — tapping a menu, opening an accordion — and the page visibly responding. A site can appear fully loaded while still being unresponsive underneath, usually because it is busy running scripts.
Aim for: under 200 milliseconds. In lab tests you will often see this reported as Total Blocking Time instead, which is a close proxy.
Curious where your site stands?
Run Google’s official PageSpeed check on your own site and see every one of these metrics for mobile and desktop, colour-coded so you can tell at a glance what needs attention.
Two more you will see
- First Contentful Paint — when the very first thing appears. Useful as an early warning: if this is slow, everything after it will be too.
- Speed Index — how quickly the page fills in visually. A page that paints steadily feels faster than one that sits blank and then snaps into place.
Do these actually affect my Google ranking?
Yes, though less dramatically than some agencies imply. Core Web Vitals are a genuine ranking signal, but relevance and content quality matter more. Where speed decisively wins is after the click: two sites can rank side by side, and the faster one quietly converts far more of the same traffic.
Put another way — Vitals are worth fixing for your customers first, and for Google second. Fortunately the same work satisfies both.