When we first heard about CSS delivery optimization, we thought it sounded too technical for most WordPress users. But after seeing the dramatic speed improvements it delivered for our own sites, we realized this was something every site owner needed to know about.
The best part is that you don’t need any coding skills to implement these changes.
We’ve seen how CSS optimization can transform a sluggish website. Sites that used to frustrate visitors with slow loading times suddenly became smooth and responsive. The impact on search rankings and user satisfaction was immediate and lasting.
After years of experimenting with different CSS optimization strategies, we’ve identified 2 foolproof methods that work every time. We’ll walk you through both approaches step-by-step, so you can choose the one that fits your comfort level and technical expertise.
How WordPress CSS Delivery Affects WordPress Performance
CSS files are used to define the visual appearance of your WordPress website. Your WordPress theme contains a CSS stylesheet file, and some of your plugins may also use CSS stylesheets.
CSS is necessary for modern websites, but it’s possible for CSS files to slow down your site’s speed and performance depending on how they are set up.
Even a small delay in website speed creates a bad user experience and may affect your search rankings and conversions, resulting in less traffic and sales.
One way that CSS files can slow your website is if they need to be loaded before the page can be displayed. That means your visitors will see a blank page until the CSS file has loaded. This is known as render-blocking CSS.
Another common reason CSS files can slow your website is when they contain more code than is needed to display the visible part of the current page. That extra unused CSS code means that their load time will be longer.
The good news is you can improve your WordPress site’s performance by optimizing the way the CSS code is delivered.
That’s done by identifying the minimum CSS code needed to display the first part of the current web page. This is known as ‘critical CSS’.
This critical code is then added inline to the page’s HTML instead of in separate stylesheets so that the code can be rendered without needing to load the CSS file first.
The rest of the CSS can then be loaded after your visitors can see the contents of the page. This is known as ‘deferred loading’.
With that being said, let’s take a look at two methods to optimize WordPress CSS delivery, and you can choose the one that works best for you:
Method 1: Optimizing WordPress CSS Delivery With WP Rocket
WP Rocket is the best WordPress caching plugin on the market. It offers the simplest way to optimize your WordPress CSS delivery. In fact, it’s as easy as checking a box.
WP Rocket is a premium performance plugin, but the best part is that all features are included in their lowest plan.
The first thing you need to do is install and activate the WP Rocket plugin. For more details, see our step-by-step guide on how to install a WordPress plugin.
Once activated, you need to navigate to the Settings » WP Rocket page and switch to the ‘File Optimization’ tab.
Next, you need to scroll down to the CSS files section.
Once there, you need to check the box next to the ‘Optimize CSS delivery’ option.
This feature will intelligently identify the critical CSS needed to format the part of the web page your visitors see first. Your pages will load more quickly, and the rest of the CSS will be loaded after your visitors can see its contents.
All you need to do now is click the ‘Save Changes’ button and wait for WP Rocket to generate the necessary CSS file for all your posts and pages.
It will also automatically clear the cache for your website so that your visitors will see the new optimized version of your site instead of an unoptimized version stored in the cache.
There are plenty of other ways that WP Rocket can help you improve your website’s performance. To learn more, see our guide on how to properly install and set up WP Rocket in WordPress.
Method 2: Optimizing WordPress CSS Delivery With Autoptimize
Autoptimize is a free plugin designed to improve the delivery of your website’s CSS and JavaScript files.
While Autoptimize is a free plugin, it doesn’t have as many features as WP Rocket and takes more time to set up.
For example, it’s not able to automatically identify critical CSS like WP Rocket can. Instead, Autoptimize requires the help of a premium third-party service, which is an additional cost and requires extra time to configure.
However, it could be a good option if you are on a tight budget and don’t need all the other features of WP Rocket to speed up your site.
The first thing you need to do is install and activate the Autoptimize plugin. For more details, see our step-by-step guide on how to install a WordPress plugin.
Upon activation, you need to visit the Settings » Autoptimize page to configure the plugin settings. Once there, you need to scroll down to the CSS Options section and check the ‘Optimize CSS Code’ box at the top.
Once you do that, you need to make sure that the ‘Aggregate CSS-files’ option is unchecked and then check ‘Eliminate render-blocking CSS’.
You can now click on the ‘Save Changes and Empty Cache’ button to store your settings.
But the plugin will not work properly until you sign up for a Critical CSS account. This is a premium subscription service that will provide Autoptimize the critical CSS code it needs to optimize your WordPress CSS delivery.
To do that, navigate to the Critical CSS tab in Autoptimize’s settings. Here you’ll find the information you need to sign up with Critical CSS. You can get started by clicking the sign-up link in the third paragraph.
Once you’ve received your Critical CSS API key, scroll down to the API Key section so you can paste it into the ‘Your API key’ text box.
After that, make sure you click the ‘Save Changes’ button.
Autoptimize now has all of the information it needs to add the critical CSS inline and defer loading the stylesheets until after the page has been rendered. As a result, your website will have a faster loading speed.
FAQs About Optimizing WordPress CSS Delivery
Below are some of the most common questions we receive about optimizing WordPress CSS delivery. These should help clarify any remaining doubts you might have about implementing these optimization techniques.
1. What is CSS delivery optimization and why does it matter for WordPress sites?
CSS delivery optimization is the process of improving how your website loads stylesheets to reduce page loading times. It matters because poorly optimized CSS can create render-blocking issues, causing visitors to see blank pages while waiting for stylesheets to load. This directly impacts user experience, search rankings, and conversion rates.
2. Will optimizing CSS delivery break my WordPress theme’s design?
No, when done correctly, CSS optimization should not break your theme’s design. Both WP Rocket and Autoptimize are designed to preserve your site’s appearance while improving performance. However, we always recommend testing the optimization on a staging site first and keeping a backup of your original site before making changes.
3. What’s the difference between critical CSS and render-blocking CSS?
Critical CSS is the minimum CSS code needed to display the visible part of a webpage (above the fold content). Render-blocking CSS refers to stylesheets that prevent the page from displaying until they’re fully loaded. CSS optimization works by identifying critical CSS and loading it inline, while deferring non-critical CSS to load after the page is visible.
4. Do I need coding skills to implement CSS delivery optimization?
No coding skills are required for either method we’ve covered. WP Rocket makes it as simple as checking a box, while Autoptimize requires basic plugin configuration. Both plugins handle the technical aspects automatically, so you don’t need to write or modify any CSS code yourself.
5. How much can CSS optimization improve my site’s loading speed?
The improvement varies depending on your current setup, but we’ve seen loading time improvements of 30-50% in many cases. The exact speed boost depends on factors like your theme, plugins, hosting, and current CSS structure. Most sites see noticeable improvements in Core Web Vitals scores and Google PageSpeed Insights ratings.
6. Is WP Rocket worth the cost compared to using the free Autoptimize plugin?
WP Rocket offers more comprehensive optimization features and automatically handles critical CSS generation, making it much easier to set up and maintain. Autoptimize is free but requires a premium Critical CSS service subscription and more manual configuration. For most users, WP Rocket’s time-saving features and additional performance benefits justify the investment.
We hope this tutorial helped you learn how to optimize WordPress CSS delivery. You may also want to see our guide on how to apply CSS for specific users roles in WordPress and our expert pick of the best WordPress slider plugins.
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Jiří Vaněk
I use both plugins simultaneously because, according to the results, it has helped speed up my website. However, I have the “Optimize CSS delivery” feature enabled in WP Rocket and disabled in Autoptimize. I’ve tested on my site that these two plugins complement each other perfectly. The only thing you need to watch out for is that the same function is not enabled in both plugins at the same time. Nevertheless, together they form a powerful duo.
Dennis Muthomi
I’ve implemented WP Rocket on several client sites and can attest to its effectiveness in improving page load times.
The “Optimize CSS delivery” feature is indeed as simple as checking a box, but it’s impressive how much it can impact performance.
One additional tip I’d offer is to use a tool like GTmetrix or Google PageSpeed Insights to measure your site’s performance before and after implementing these optimizations. This can help quantify the improvements and identify any remaining issues.
Jiří Vaněk
Yes, Dennis, I do the same, with the difference that I use WP Rocket everywhere. Due to speed issues, I’ve tried all the cache plugins during my time using WordPress, and WP Rocket is unbeatable. The preload feature has helped me the most, but various minifications and code optimizations have also made a significant impact. Your recommendation is a great idea that complements the text well. However, for speed measurement, I find GT Metrix more professional and better. Especially the waterfall feature, where the entire loading process of the website is displayed in detail. It’s a great tool, free at its core, and it’s fantastic that you mentioned it here.