Most Important Website Performance Metrics You Need to Understand

How much time does it take to load a web page? How long does it take to download a file from a server? These questions are important because they affect user experience. If a site takes too long to load or loads slowly, visitors will leave before they get their answers.

When it comes to website performance, there are two key measurements: response time and page loading time. Response time measures how long it takes for a visitor’s browser to send a request to a web server. Page loading time refers to the amount of time between when a visitor clicks on a link and when the requested page appears.

To improve website performance, you should focus on reducing both response time and page loading times. There are several ways to do this, such as optimizing images and using caching techniques. In this article, we’ll discuss these methods and explain how to measure them.

The First Step in Improving Web Site Performance

Response Time

Response time is measured by recording the amount of time between a browser’s clicking on a link (e.g., “click here”) and when that link actually works, such as displaying text or images from a web server. It includes three different types of delays: 1) round-trip delay, 2) first-hand delay, and 3) third-party delay. The total amount of time it takes for the browser to receive the answer it wants reflects all of these delays.

A quick rule of thumb is that if a site takes more than one second to respond after someone clicks a link, then it probably has poor response time. A typical page load time can range anywhere from 500 milliseconds to 10 seconds. This means that most websites with reasonable traffic fall into the 5-second category. To determine whether your response time is acceptable, use an online service such as

Page Loading Time

The first step in improving web page performance is to reduce the amount of time it takes to display content. Most sites have at least four main components: HTML code (the actual message), CSS files, JavaScript objects, and image files. Images play an important part in overall page performance because they may contain large amounts of data.

Fortunately, the size of the image itself often doesn’t matter very much; what matters is the number of bytes needed to store each pixel in the image. Each byte represents the same raw information, so it’s not like you’re saving tons of space by using a smaller version of a picture. For example, imagine a high-resolution photo stored in various formats: JPEG, GIF, PNG, TIFF, BMP, etc. Which would you prefer? That depends on the quality of the original photograph and your memory capacity.

So while larger pictures require more disk space, they also load faster.

The next question is which format to use. Many people choose either JPEG or PNG because they offer better compression results than other formats. However, although the best compression technique varies based on the type of image, all modern browsers support GIF, PNG, and JPEG images. So choosing one format over another is just personal preference. Remember, however, that the fewer bytes used to represent any particular element, the faster it will be downloading.


Another way to reduce page load time is to cache previously downloaded objects. When you visit a site, many resources need to be loaded from the web server before the page displays. If you click on a link, those requests are sent to the server with the accompanying URL. The server responds with the HTML file containing the text you want and includes links to other files. These include external stylesheets, scripts, and even Flash video. Once everything is done, the browser parses the HTML to put together the layout.

If you’ve visited a page recently, chances are the server hasn’t changed much since the last time you viewed the website. In this case, the latest version of the script, stylesheet, and other files are already cached on the client’s system. When the browser needs to access them again, there’s no need to download anything. As long as they haven’t been altered since the previous visit, they’ll appear almost instantly. And since they’re now available locally, they won’t have to go back to the server, reducing bandwidth usage and potentially speeding up the whole process. This is particularly helpful if the site uses lots of dynamic elements, such as forms, menus, and graphics.

In addition to this “local caching,” some browsers allow developers to instruct them to keep certain things on their own hard disks instead of having to request them from the server every time. This concept is called “offline” caching and can save significant amounts of bandwidth. However, offline caching has its limitations: for example, users must be connected to the Internet when they access websites that use it. It also applies only to static pages — once-dynamic changes have taken place, online caching no longer works.

One important caveat: Some servers make it possible to preload different versions of a given resource depending on the user’s location or connection speed. For example, a server could decide to display an alternate stylesheet for slow connections and then switch back to regular style sheets once connectivity improves. While these strategies can help improve latency when there’s a network problem, they’re rarely worth the extra effort and complication.

Preloading content for later

If your computer isn’t fast enough to view a site right away after opening it in your browser window, it may not make sense to wait until the content loads completely before navigating elsewhere. Instead, the browser could start loading data while waiting for the main page to finish rendering. Once the page starts displaying, the browser stops fetching new information and begins to display the page as quickly as possible. A popular method of doing so is through what’s known as a “prefetch.”

Prefetching is essentially an early warning system. When something needs to load later, the browser takes note of it beforehand. Then, when it actually happens, the computer is less likely to freeze. Since prefetching can take place either during page render time or at times set in advance (such as when entering URLs into search engines), it might not happen at all times. But it does work well if the person performing the task isn’t busy browsing around the Web at the moment.

The best way to find out whether prefetching will benefit your particular situation is to monitor how much data your browser downloads on a typical day. Ideally, you should test this periodically over multiple days: One week could give very different results than one month.

For example, Google Chrome displays a warning message when you enter a string like in its address bar. This means that the browser is about to try to load the homepage of the New York Times. If your computer is able to handle the task, the warning message disappears immediately; otherwise, the page appears slowly and briefly and then the warning message reappears. The behavior is similar to any other type of URL. To avoid freezing the page, simply press Enter to open the link.

On most modern computers, the default setting for Prefetch is off. To turn it on, select File → Preferences → Advanced → Network. On older systems, you may need to change settings by clicking Tools → Options → General → Browsing History → Settings.

You should understand how browser caching affects your organization’s website development projects because it has a major impact on optimization and usability. The solution depends on which kind of website you’re developing. Content management systems, for instance, have built-in features that cache static pages for extended periods. In contrast, eCommerce sites must be kept up to date manually to keep customers shopping with no interruptions from broken links. Here are some of the more common methods used today: Static Caching An ideal practice would be to always build websites without using database queries. Unfortunately, it doesn’t always work that way, especially when building dynamic websites.

In addition, you’ll want to use the cache option in your favorite web framework’s configuration file. That lets you specify that certain paths and files should never expire. Your options include Apache’s.htaccess files, Nginx’s http_vary directive, and the equivalent directive in.NET applications. By limiting access to static resources, the request processing overhead is reduced and overall responsiveness improves.

How to Improve Site Speed

While there are many ways to speed up a site, there is only one thing you cannot do anything about – the Internet itself. Most people tend to blame the slowdown on their host, but sometimes the problem really lies with the design of the site itself. Understanding these issues will help save money and reduce headaches in the long run.

There are several tools available that can analyze your web traffic and provide tips for speeding up a site. If you plan to serve a lot of images or large files, consider hosting them externally so they don’t slow down your site. There are plenty of image hosts that let you upload an unlimited number of images and set how often they’re rotated.

To optimize images further, consider using CSS filters instead of background images. Filters are more efficient and responsive than background images. And if you do decide to add a background image, make sure it’s transparent or at least semi-transparent. Avoid creating solid background colors as well unless you need to create a specific effect. Some browsers ignore color backgrounds completely. These include IE6,7 and 8, Safari 5, and Microsoft Edge.

The first step is to find out what actually slows down your site. If you know that it’s because you’re loading too much JavaScript before displaying the content, then focus your efforts on optimizing scripts that actually perform the core functions of your application. Once you’ve found the culprits, start testing different approaches to see which ones offer the best performance while still meeting all of your requirements. For more information, check out Google’s PageSpeed insights tool.

With this approach, you should see significant improvements within a week or two. Afterward, continue focusing on enhancing individual aspects of your page once you reach each new level of optimization. This process takes time and effort and requires patience. But it pays off over time by making your website faster and smoother to interact with.

Optimizing Images

When most designers think of image optimization, they think of compressing their graphics files. They might also get confused and think that they should remove any unnecessary tags or comments. Those things can certainly help save storage space and increase download speeds, but they won’t have an impact on performance until after those images load into memory. At that point, you’ll need to prioritize compression or eliminate redundant data.

For example, it can be helpful to compress images directly in Photoshop rather than uploading them to an online service like While many image editing programs automatically optimize images, some designers prefer to take complete control of the process themselves. To ensure that you get the highest quality output, use high settings when exporting the optimized file.

Include HTML5 Tags When It Makes Sense. However, these tags may not always be useful. For instance, you might want to display a custom icon to indicate an active link. Or perhaps you’d like to show a rotating image instead of a static one. In those cases, you’d simply leave the tag out.

Instead of optimizing every element, focus on elements that are critical to your functionality. In other words: Don’t worry about minification or compression until you know for certain that a given element has no effect on performance.

Use the Right Image Types. The biggest mistake webmasters make when designing pages is choosing the wrong type of image to load. Instead of worrying about pixel counts, pay attention to the ratio between textual content and images. That will give you a better idea of how heavy the page will become once it loads.

If text dominates the page, it’s probably safe to assume that using large images will result in slower load times. Conversely, if there are lots of small graphic elements mixed with text, opt for smaller images where possible.

Check Your Scripting. There are several ways in which scripting can slow down sites. Most developers rely on unobtrusive script code to modify page behavior without affecting page performance.

However, the problem arises whenever a browser encounters a script that adds extra network requests to the request/response cycle. These can slow the overall pace of events significantly depending on the number of resources added to the mix. Make sure to carefully consider the effects of all of your JavaScript-based functionality on page speed.

While this topic could easily fill up its own article, I’m confident that you’ve got enough material from my previous tips on layout design and imagery to keep your website performing at peak efficiency. Keep in mind that all of these techniques come together to create a unified experience that enables users to interact smoothly with your content and navigate the site quickly. By paying close attention to as many details as possible, you ensure that people can enjoy the full benefit of your website.

The above are just a few ideas to start thinking about when it comes to improving your website’s performance. As long as you’re willing to put in the work and dedicate time to analyzing your results, it shouldn’t take more than a day or two before you see significant improvements. By focusing on what really matters — user experience, not speed alone — you’ll set yourself apart from the competition.

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