Google PageSpeed Insights is a free tool that analyzes the performance of a website and provides recommendations for improving loading speed and user experience.
After testing a website, the tool assigns a score between 0 and 100 and highlights areas that may require optimization.
You can access the tool here:
Table of Contents
Mobile vs Desktop Results
PageSpeed Insights performs separate tests for:
- Mobile devices
- Desktop devices
Because the evaluation criteria differ, it is common to see significantly different scores between the two versions.
For example:
- A website may score highly on desktop devices but perform poorly on mobile devices.
- A mobile score may be lower due to slower simulated network conditions and stricter performance requirements.
For this reason, both reports should be reviewed independently.
Understanding the Performance Score
The overall score is displayed on a scale from:
0 – 100
General interpretation:
| Score | Performance |
|---|---|
| 90–100 | Good |
| 50–89 | Needs Improvement |
| 0–49 | Poor |
The score is calculated using Google’s Lighthouse testing methodology.
Key Performance Metrics
First Contentful Paint (FCP)
Measures how quickly the first visible content appears on the page.
Examples of content include:
- Text
- Images
- Icons
- Background graphics
A lower value indicates that visitors begin seeing content sooner.
Speed Index
Measures how quickly visible content is rendered during page loading.
This metric focuses on the visual progression of the page rather than just the first visible element.
Lower values are better.
Largest Contentful Paint (LCP)
Measures the time required to load the largest visible element on the page.
This is one of the most important performance metrics.
The largest element is often:
- A hero image
- A banner
- A featured image
- A video
- A large text block
Poor LCP scores are frequently caused by:
- Large images
- Unoptimized videos
- Slow server responses
- Render-blocking resources
Time to Interactive (TTI)
Measures how long it takes before the page becomes fully interactive.
A page may appear visually complete while still processing JavaScript in the background.
A lower TTI means visitors can interact with:
- Menus
- Buttons
- Forms
- Search fields
more quickly.
Cumulative Layout Shift (CLS)
Measures visual stability during page loading.
A high CLS score means page elements move unexpectedly while the page loads.
Examples include:
- Buttons shifting position
- Text jumping downward
- Advertisements loading and pushing content
Poor CLS negatively impacts user experience and may cause visitors to click the wrong element.
Opportunities Section
The Opportunities section contains recommendations that can potentially improve performance.
Common examples include:
Remove Unused CSS
Many websites load CSS styles that are not required on every page.
For example:
- Homepage styles loading on the contact page.
- WooCommerce styles loading on non-store pages.
Removing unused CSS reduces file size and improves loading speed.
Minify CSS and JavaScript
Minification removes:
- Spaces
- Line breaks
- Comments
from CSS and JavaScript files.
Example:
body {
color: black;
}
becomes:
body{color:black}
This reduces file size and speeds up downloads.
Enable Compression
Compression reduces the size of files transferred between the server and the browser.
Common compression methods include:
- Gzip
- Brotli
Compression can significantly reduce:
- HTML files
- CSS files
- JavaScript files
Optimize Images
Image optimization is often one of the easiest ways to improve performance.
Common issues include:
- Uploading images at 4000px resolution when displayed at 400px.
- Using uncompressed formats.
- Serving unnecessarily large files.
Recommended formats include:
- WebP
- AVIF
Lazy Loading
Lazy loading delays the loading of images and media until they become visible on the screen.
Benefits include:
- Faster initial page load.
- Reduced bandwidth usage.
- Better mobile performance.
Diagnostics Section
The Diagnostics section provides additional technical information about performance bottlenecks.
Although these items do not directly affect the performance score, they often highlight areas where further optimization is possible.
Examples include:
- Long-running JavaScript tasks.
- Excessive DOM size.
- Third-party script impact.
- Render-blocking resources.
Audits and Recommendations
Each website receives different recommendations depending on:
- CMS platform.
- Theme structure.
- Plugins.
- Custom code.
- Images and media.
- Third-party integrations.
Clicking any recommendation within PageSpeed Insights provides detailed explanations and potential solutions.
Common Causes of Poor Scores
The most frequent performance issues are:
- Oversized images.
- Excessive plugins.
- Unoptimized JavaScript.
- Unused CSS.
- Lack of page caching.
- Slow server response times.
- Too many external scripts.
- Excessive advertisements or tracking tools.
WordPress Optimization Tips
If your website runs on WordPress, consider:
- Using page caching.
- Optimizing images before upload.
- Enabling lazy loading.
- Removing unused plugins.
- Using a CDN.
- Minifying CSS and JavaScript files.
- Keeping themes and plugins updated.
Important Reminder
A high PageSpeed score does not automatically guarantee a better user experience.
Likewise, a website with a lower score may still feel fast and responsive to visitors.
PageSpeed Insights should be viewed as a set of optimization guidelines rather than an absolute measure of website quality.
Lighthouse Score Calculator
Google’s Lighthouse score calculation can be explored using:
This tool shows how different performance metrics contribute to the final PageSpeed score.
Summary
Google PageSpeed Insights helps identify opportunities to improve website performance by measuring:
- First Contentful Paint (FCP)
- Speed Index
- Largest Contentful Paint (LCP)
- Time to Interactive (TTI)
- Cumulative Layout Shift (CLS)
Pay particular attention to:
- Image optimization
- CSS and JavaScript minification
- Compression
- Lazy loading
- Removing unused resources
The recommendations provided by the tool can help improve loading times, user experience, and search engine visibility.