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How To Measure And Optimize Page Load Time

Loading the content of a web page quickly not only matters to your visitors but is also a Google ranking factor that impacts your SEO. So optimizing page load times can also bring you more traffic.

This article looks at what page load time means, how to measure it, and how to optimize the performance of your website.

What is page load time?​

Page load time measures how long it takes for the contents of a website to show up in the user’s browser.

The loading process of a website will consist of multiple milestones, for example starting to show text or displaying a hero image.

There isn’t one single metric that measures page load time. When you see page load times reported make sure what specific metric is being measured.

We recommend focussing on the Largest Contentful Paint metric.

Filmstrip view showing the rendering progress and milestone markers of a website

Why does the page load process consist of multiple milestones?​

Loading a web page normally consists of many different steps, for example:

  • Loading the document HTML
  • Loading CSS stylesheets
  • Loading images
  • Loading a chat widget from another website
  • Running JavaScript code

To make the browsing experience better, browsers try to display content as soon as it’s ready. Content usually appears gradually on the page.

There’s no single time when the page is “loaded”. A page might have loaded 98% of its contents except for a small footer image and an analytics script – but this doesn’t impact the user so we wouldn’t say that the page hasn’t loaded yet. Counting the final stretch to 100% as “the” loading time isn’t what we want to measure, since users can use that page just fine before that time.

Instead there are multiple metrics that can be considered:

It’s also worth mentioning that the page load times aren’t absolute. They vary depending on the device type (desktop/mobile), browser, user location, internet connection and many other factors.

Why focus on the Largest Contentful Paint?​

There are a few reasons why LCP is the best starting point for page load time optimization:

  • It measures how soon the user can see content, rather than measuring a technical detail
  • It focuses on the main page content
  • It’s one of the three Core Web Vitals that impact Google rankings

What is a good page load time?​

According to Google’s Core Web Vitals, a Largest Contentful Paint of 2.5 seconds or below is a good page load time.

Page load times up to 4 seconds are acceptable, and google will flag them as “Needs Improvement”.

A page load time over 4 seconds is slow and Google will rate it as Poor”.

Visualization showing rating thresholds for the Largest Contentful Paint metric.

Does page load time affect SEO?​

Yes, page load times can have an impact on search engine rankings.

While content quality is more important than page speed, Google uses a set of page experience metrics as part of their ranking algorithm.

In addition to the Largest Contentful Paint metric, Google also looks at Cumulative Layout Shift and First Input Delay.

How do you measure page load time?​

You can measure page load time using a free tool like Google’s PageSpeed Insights or the DebugBear Speed Test.

Simply enter your website URL to see your page speed metrics and get recommendations on how to optimize your website performance.

Often you’ll see a mix of lab and field data:

  • Lab data is collected on demand in a controlled test environment
  • Field data is collected from real users

Field data is often based on the Chrome User Experience Report (CrUX) which aggregates data from the last 28 days.

Here’s an example of what part of a website performance report might look like.

Page speed report showing performance metrics and overall scores.

Right off the bat you can see that optimizing the Largest Contentful Paint metric of this page could help it rank higher in Google. There are other metrics to keep an eye on as well, and these are all highlighted in red.

You can also see a visualization that shows how the page renders gradually.

Filmstrip view showing rendering progress of a website

In many cases there’ll be performance recommendations specific to your website.

List of performance recommendations for a website

A request waterfall visualization can also help identify potential performance improvements.

Request waterfall showing blocking requests and request timings.

How to monitor page load time​

Continuously measuring page load time not only lets you check if your optimizations are working but will also alert you if your site got slower.

DebugBear can monitor site speed over time, including the Core Web Vitals metrics that impact search engine rankings.

Dashboard with site speed monitoring data

How do I reduce page loading time?​

You can reduce page loading time by looking at 3 big components:

  • Server response times
  • Download sizes
  • Rendering time

To make your website load fast you need to process requests quickly on the server, use image and text compression to reduce file sizes, and minimize the amount of JavaScript on your page.

Step 1: Optimize server response times​

Once a user clicks on a link or type a URL, the browser requests that page from a remote server. It then waits until the server responds with the contents of the page.

This part of the page load process is represented by the TTFB (Time To First Byte) metric. In addition to the time spent processing the request on the server, TTFB also includes time spent looking up the server IP address via DNS and establishing a secure server connection of TCP/SSL.

Breakdown of the Time to First Byte metric

If you notice that your TTFB is too high, you can focus on this part of the loading process. A TTFB under 0.8 seconds is considered good by Google. If it’s higher than 1.8s, it’s considered poor.

Now let’s see how you can improve the TTFB.

Reducing processing time on the server​

HTML documents typically aren’t static but are generated by the server for each request. For example, different users will be served different page contents, or the content of a news website will change throughout the day. Generating the HTML involves loading data from a database and using templates to construct the page.

Caching all or parts of the HTML can speed up server responses. Instead of regenerating the response every time the server will save the generated response and reuse it later on.

If you’re using a content management system like Wordpress make sure that you aren’t using too many plugins, as these can slow down your website. For simple websites you could also consider switching to a faster solution like a static site generator.

Another key factor to processing times is the hosting provider. If your hosting provider is too slow, you’ll need to switch hosting plans or pick a different provider.

Physical distance between client (browser) and server​

No matter how fast your server is, there is still the time it takes for the request to travel from the visitor’s browser to your servers, and then for the content to be sent back.

For example, if your server is based in New York but some of your visitors are in Tokyo, then it will take around 180 milliseconds for each round trip between client and server. Typically at least 3 round trips are needed to create a connection and make a request. So this factor alone could cause a delay of 0.5 seconds just for a single request.

Content Delivery Networks (CDNs) can address this issue. They have locations in hundreds of places across the world, so round trip times will be much lower.

Strep 2: Optimize download sizes​

Once your server has provided the page HTML for the website it will start downloading other content on the page. For example, it will load render-blocking stylesheets and download images.

The amount of available bandwidth and latency determine how long it takes to download a given file. Larger files will take longer to download.

You can often see pages render gradually as more content becomes available.

Gradual rendering progress of a website

There are a few things you can do to reduce download sizes and load resources efficiently.

Image, video, and text compression​

Compression means making a file smaller without changing its contents. For images the image quality can also sometimes be reduced.

Using modern image formats like WebP or AVIF can reduce download sizes without impacting image quality. You can also reduce the resolution of your images, or load different images depending on the device size using the srcset attribute.

Text files like HTML, CSS, and JavaScript can be compressed with algorithms like gzip and brotli.

There are many WordPress plugins and tools to automatically compress resources, for example WP Rocket.

Optimize resource priorities​

Not every resource on your website is equally important. You can improve the LCP and the overall user experience by controlling when to load which assets. That way bandwidth is allocated to the most important content.

For example, you can use Priority Hints to tell the browser that a hero image on your website should be prioritized.

Images further down on the page can be lazy loaded, so they don’t compete for bandwidth with more important content.

If a script isn’t important it should be loaded asynchronously with the async keyword.

You can also preload important resources if the browser doesn’t discover them right way.

Step 3: Reduce rendering times​

Your visitor is connected to your server and they’ve downloaded your important resources. But there is still some work to do.

The browser needs time to process resources, display the layout, to load sliders, widgets, or render dynamic content. Rendering this content quickly is particularly important in mobile browsers, since they have less processing power.

You can measure the impact of CPU processing page loading times with metrics such as Total Blocking Time (TBT) and Time To Interactive (TTI).

Identify what code is slowing down your website​

CPU timelines in DebugBear or the Chrome DevTools Performance tab will tell you whether this is slowing down your website and what tasks the browser is spending time on.

CPU timeline on a website

Use less JavaScript​

When adding JavaScript to your page you need to factor in the processing power that it will take. Notifications, animations, sliders, tracking codes, are all really useful. But be mindful of how much they can cost in terms of conversions, rankings, and revenue if they slow your site down.

Sometimes the best solution is to just remove them.

Conclusion​

This article looked at how to measure page load time and what three factors impact page performance. You can now use this knowledge on your own website to optimize the Largest Contentful Paint and deliver a better user experience.