Website speed and Core Web Vitals: a complete guide
Updated: · Webu
Core Web Vitals are Google’s three metrics for measuring real user experience: LCP (loading of the main content, good under 2.5 seconds), INP (response to user interaction, good under 200 milliseconds) and CLS (visual stability, good under 0.1). Google recommends meeting these thresholds for 75% of visits, measured separately on mobile and desktop.
- LCP
- ≤ 2.5 seconds
- INP
- ≤ 200 milliseconds
- CLS
- ≤ 0.1
- Measured at
- the 75th percentile of visits
What are the three Core Web Vitals metrics?
The thresholds come from web.dev’s official recommendations. Google suggests assessing the 75th percentile of visits: a metric is “good” if at least 75% of visits meet the threshold.
| Metric | What it measures | Good result |
|---|---|---|
| LCP (Largest Contentful Paint) | How quickly the main element of the page appears | Under 2.5 seconds |
| INP (Interaction to Next Paint) | How quickly the page responds to taps and typing | Under 200 milliseconds |
| CLS (Cumulative Layout Shift) | How much the page “jumps” while loading | Under 0.1 |
Why is website speed a business issue?
On a slow website people wait, get frustrated and often simply go back to search and a competitor. Mobile matters most: many visitors open websites on their phones over mobile data. Google’s guidance names a good page experience as one of the foundations of success in search.
How do you measure website speed?
- PageSpeed Insights (pagespeed.web.dev): free, shows both lab data and real-user data when the site has enough traffic
- Google Search Console: the Core Web Vitals report for the whole site
- Lighthouse in Chrome DevTools: detailed technical analysis for developers
- Webu’s free SEO audit: a quick assessment of speed, SEO and security
Why is a website slow?
- Unoptimized images and videos: files that are too large and old formats (JPG and PNG instead of WebP and AVIF)
- Heavy templates and too many plugins loading dozens of scripts on every page
- CSS and JavaScript that block the page from rendering
- Slow hosting on a server far away from users
- Fonts that hide text until they load
- Elements without set dimensions, which make the page jump while loading (CLS)
How does Webu improve website speed?
Speed is part of the mandatory quality check on every Webu project. A practical example from our own website: we prepared separate, lighter homepage videos for mobile, converted images to WebP and gave the main element high loading priority. We measure quality instead of just claiming it.
- Compressed images in modern formats
- A separate, lighter video for mobile
- Preloading the main element (LCP)
- Fewer and deferred scripts
- Fast hosting and a CDN
Frequently asked questions
What are Core Web Vitals?
Core Web Vitals are Google’s three metrics for assessing real user experience: LCP (loading speed), INP (responsiveness) and CLS (visual stability).
What is a good LCP?
According to web.dev, LCP is good when the main element of the page appears within 2.5 seconds of the page starting to load.
What did INP replace?
In 2024 INP replaced FID (First Input Delay) and now measures how quickly a page responds to all user interactions during a visit.
How can I check my website speed for free?
Use PageSpeed Insights or Webu’s free SEO audit, which checks speed along with SEO and security.
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