If you've ever run your site through Google's PageSpeed Insights, you've seen a soup of three-letter initials — FCP, LCP, CLS, INP — each attached to a green, yellow, or red score. Those aren't vanity metrics. They're the specific numbers Google uses to decide whether your site shows up above or below the competition.
The good news: you don't need to understand them the way a developer does. You just need to know what each one measures, what "good" looks like, and what to fix when you're in the red. That's this article.
Why these four metrics exist
In 2020, Google introduced Core Web Vitals — a set of user-experience metrics that would become part of its ranking algorithm. The idea was simple: sites that load fast, render predictably, and respond when tapped should rank higher than sites that don't. No more hiding behind keyword tricks if the experience itself is broken.
Today, Google measures four numbers that matter for ranking:
- FCP — First Contentful Paint
- LCP — Largest Contentful Paint
- CLS — Cumulative Layout Shift
- INP — Interaction to Next Paint
Let's take them one at a time, in plain English.
First Contentful Paint (FCP) — "something showed up"
FCP measures how long it takes, after a visitor clicks your link, for anything to appear on their screen. Not the full page — just the first piece of content, whether that's a headline, a logo, or a background color.
Think of it like walking into a restaurant. FCP is how long you stand at the door before you're acknowledged. If it's instant, you feel welcomed. If it's 4 seconds of staring at nothing, you're already annoyed.
Target:
- Green: under 1.8 seconds
- Yellow: 1.8 – 3 seconds
- Red: over 3 seconds
What hurts FCP: huge CSS files that have to download before anything can render, slow hosting, JavaScript-heavy page builders that block the initial render, and blocking third-party scripts (chat widgets, analytics tags, old tracking pixels).
Largest Contentful Paint (LCP) — "the main event appeared"
LCP measures when the biggest visible thing on the page finishes loading. Usually that's a hero image, a headline, or a video poster. This is the moment the visitor feels the page is actually "there."
Back to the restaurant: FCP is the host saying "welcome." LCP is the menu being handed to you. Until you have the menu, you can't decide anything.
Target:
- Green: under 2.5 seconds
- Yellow: 2.5 – 4 seconds
- Red: over 4 seconds
LCP is the Core Web Vital most tightly correlated with ranking. If you only fix one number, fix this one. We cover the practical fixes in our separate piece on getting your site under 1-second load.
Cumulative Layout Shift (CLS) — "the page stopped jumping"
CLS measures how much your page moves around after it starts rendering. You've felt this one: you go to tap a button, a banner ad loads above it, the button slides down, and you accidentally tap something else. That's layout shift — and Google hates it.
Unlike FCP and LCP, CLS isn't measured in seconds — it's a unitless score between 0 (perfect) and 1+ (terrible).
Target:
- Green: under 0.1
- Yellow: 0.1 – 0.25
- Red: over 0.25
What hurts CLS: images without declared dimensions, web fonts swapping after the page renders (the classic "everything moved down an inch"), ads injected above existing content, slow-loading embeds like YouTube thumbnails or tweet embeds.
Interaction to Next Paint (INP) — "the site feels responsive"
INP is the newest Core Web Vital, replacing the older "First Input Delay" in early 2024. It measures how long the page takes to visibly respond when a visitor taps, clicks, or types. Any delay over about a quarter-second makes a site feel "heavy" or broken.
Target:
- Green: under 200ms
- Yellow: 200 – 500ms
- Red: over 500ms
INP problems are almost always caused by too much JavaScript running on the page. If your site was built on a heavy page builder (Elementor, Wix, Squarespace on a themed template), INP is usually the hardest metric to get green — because the page builder runs its own scripts on every interaction.
How to check all four on your own site
- Go to pagespeed.web.dev
- Paste your homepage URL
- Click Analyze
- Scroll to the "Core Web Vitals Assessment" block at the top
You'll get either "Passed" (green) or "Failed" (red) for real-user data from the last 28 days — what Google calls field data. Below that, you'll see lab-data scores for a simulated test run. Both matter, but field data is the one Google uses for ranking.
When not to obsess
A few honest words: once you're green across all four, there are diminishing returns. Shaving FCP from 1.2s to 0.8s feels great but won't change your ranking. Moving LCP from 5s to 2s will.
The Core Web Vitals bar is fundamentally a "don't be bad" bar — pass it, and Google stops penalizing you. Dominating beyond that comes from everything else: content, reviews, backlinks, Google Business Profile.
For the specific fixes that move Core Web Vitals numbers, read our companion piece on getting your business website under 1-second load, or the seven local ranking signals that matter more than shaving milliseconds.
The short version
- FCP under 1.8s — something paints fast
- LCP under 2.5s — the main content paints fast
- CLS under 0.1 — nothing shifts around
- INP under 200ms — it responds when tapped
Hit all four and Google has nothing to punish you for on the performance side. Miss them, and it doesn't matter how good your copy is — your competitors with simpler sites are outranking you.
Every site we build at Premium Sites passes all four Core Web Vitals on day one — it's baked into the stack, not bolted on. See recent builds or get a free audit of yours.