Key takeaways
- Core Web Vitals measure loading, responsiveness and visual stability.
- Field data from real visitors matters more than a single lab test score.
- Large images, heavy scripts, web fonts and slow hosting are common causes.
- Prioritise fixes on the pages that matter most to your business.
In this article
What the current metrics measure
Core Web Vitals are a set of metrics Google uses to describe real-world user experience. At the time of writing, they are:
| Metric | What it measures | Good threshold |
|---|---|---|
| Largest Contentful Paint (LCP) | How quickly the main content loads | 2.5 seconds or less |
| Interaction to Next Paint (INP) | How quickly the page responds to interactions | 200 milliseconds or less |
| Cumulative Layout Shift (CLS) | How much the layout moves unexpectedly | 0.1 or less |
Metrics and thresholds can change, so check Google's Web Vitals documentation for the latest guidance.
Field data versus lab tests
Field data comes from real visitors using your site on their own devices and networks. It shows what customers actually experience.
Lab data comes from a controlled test, such as a single PageSpeed Insights run. It is useful for diagnosing problems but does not represent every visitor.
Use field data to understand the scale of a problem and lab tests to investigate causes.
Common causes of poor performance
- Oversized images, especially large hero images.
- Too many scripts from plugins, chat widgets and tracking tools.
- Web fonts that block text from appearing.
- Content that loads late and pushes the layout around.
- Slow or overloaded hosting.
- Page builders that output unnecessary code.
Image, font, script and hosting improvements
- Images: resize to the dimensions needed, use modern formats such as WebP, set width and height, and lazy-load images below the fold.
- Fonts: limit the number of weights and use font-display settings that show text quickly.
- Scripts: remove unused plugins and defer non-essential scripts.
- Layout stability: reserve space for images, embeds and banners.
- Hosting: choose hosting suited to your traffic and use caching where appropriate.
How to prioritise fixes by page value
Start with the pages that bring in customers: the home page, main service pages, key landing pages and checkout. A small improvement on a high-traffic page usually matters more than a perfect score on a rarely visited page.
Monitoring after launch
Performance can degrade as content, plugins and tracking tools are added. Review Core Web Vitals in Google Search Console regularly and check new pages before launch. A website maintenance plan can include routine performance checks.
See our website design and SEO services, or ask us to review your site's performance.
Frequently asked questions
Do Core Web Vitals affect search rankings?
Google uses page experience signals, including Core Web Vitals, as part of its ranking systems, but relevant, helpful content remains far more important. Treat performance as a user experience priority.
Why does PageSpeed Insights show different scores each time?
Lab tests vary with network and device conditions. Field data from real users, where available, gives a more reliable picture over time.
Is a perfect score necessary?
No. Aim for good real-world experience on key pages. Chasing a perfect lab score can waste effort on changes visitors will not notice.
Can you improve our website speed?
Yes. We review performance, identify the main causes and prioritise practical fixes, from image optimisation to hosting and code improvements.
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Melbourne Design Studio is a design and development studio in Truganina, Melbourne, with more than 20 years of design and user experience work. Our team plans, designs and builds websites, apps, brands and campaigns, and writes these guides to help business owners make informed decisions.
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