Decoding Web Vitals
LCP, INP, CLS — Google's performance metrics sound complicated, but they all boil down to one thing: does your site feel fast?
If you’ve ever asked an agency about your website’s performance and walked away more confused than when you started, this one’s for you.
Core Web Vitals are what Google uses to measure how a page feels to use — not just how fast it technically loads, but whether it’s smooth, stable, and responsive. They’re a confirmed ranking factor, which means they affect where you appear in search results. They also affect whether visitors stay or leave.
The three metrics you need to know are LCP, CLS, and INP. Here’s what they actually mean.
LCP — Largest Contentful Paint
What it measures: How long it takes for the main content of your page to appear.
Specifically, this is the time from when a user navigates to your page to when the largest visible element — usually a hero image, a big heading, or a featured photo — finishes loading.
Why it matters: Visitors don’t experience “time to first byte” or “fully interactive”. What they experience is: when can I actually see something?
The target: Under 2.5 seconds.
2.5s
target — the point by which your main content should be fully visible
Common causes of poor LCP:
- Large, unoptimised hero images
- Fonts blocking rendering
- Slow server response times — a surprisingly large number of local sites built on Wix are hosted in the US, which affects load speed and can skew how Google compares you against other local businesses
- Third-party scripts loading before your content
Quick wins: Compress and convert images to WebP. Use lazy loading — rather than loading everything at once, images load as the visitor scrolls to them. Upgrade your hosting if your server response time exceeds 600ms.
CLS — Cumulative Layout Shift
What it measures: How much the page visually jumps around as it loads.
You’ve experienced bad CLS: you’re about to tap a button and suddenly an image loads above it, pushing everything down, and you tap the wrong thing. CLS quantifies how much of that instability your page has.
Why it matters: Layout shifts are jarring and lead to accidental clicks, missed content, and a general feeling that the site is unstable. Google penalises pages that cause significant layout shifts.
The target: A score of less than 0.1.
0.1
maximum CLS score — above this Google considers your page visually unstable
Common causes of poor CLS:
- Images without defined width and height attributes
- Ads or embeds that load late and push content down
- Web fonts that cause text to reflow when they load (known as FOIT/FOUT)
- Dynamic content injected above existing content
Quick wins: Always set explicit width and height on images. Reserve space for ads and embeds with CSS aspect-ratio. Use font-display: swap for web fonts and define fallback font metrics to minimise reflow.
INP — Interaction to Next Paint
What it measures: How quickly the page responds to your input.
INP replaced FID (First Input Delay) in March 2024. Where FID only measured the delay before a browser started processing your first interaction, INP measures the full duration of every interaction — clicks, taps, key presses — and reports the worst-performing one.
In plain terms: when you click something, how fast does something happen?
Why it matters: A slow INP feels laggy and unresponsive. Even if a page loads quickly, a 500ms delay every time you click something makes it feel broken.
The target: Under 200 milliseconds.
200ms
target — tap or click something and the page should react within this window
Common causes of poor INP:
- Heavy JavaScript running on the main thread
- Unnecessary third-party scripts (chat widgets, ad networks, analytics bundles)
- Long tasks blocking the browser from responding to input
Quick wins: Audit your JavaScript. Remove scripts you don’t need. Break up long tasks using requestIdleCallback or async scheduling. Defer non-critical scripts.
How to measure your Core Web Vitals
- Google PageSpeed Insights Enter your URL at pagespeed.web.dev and get a full breakdown of your scores. Focus on the mobile results — that’s where most local traffic comes from and where scores tend to be weakest.
- Chrome DevTools / Lighthouse Press
Ctrl+Shift+Ito open DevTools, go to the Lighthouse tab, and click Analyse page load. Gives you a full report with specific recommendations, and works on pages that aren’t publicly live yet. - Google Search Console If you’ve set it up, it has a dedicated Core Web Vitals report showing which URLs are failing and why — based on real user data, not just a lab test.
What a “good” score means in practice
Key takeaway
Passing Core Web Vitals doesn’t automatically put you at the top — but failing them can actively hold you back, and a slow, unstable site loses visitors regardless of where you rank.
The investment in fixing performance pays back in multiple ways: better rankings, lower bounce rates, and more visitors who actually complete their journey through your site.
Ready to act on this?
Get a performance audit
We identify and fix Core Web Vitals issues as part of our development work — and can usually pinpoint the biggest wins in a single session.