Web Performance 101: Page Size Metrics (Total Downloaded Bytes)

This blog will be a series of posts that will discuss some of the most important performance metrics. We will analyze real-time data and compare the top performing websites with those at the lower end of the spectrum. Best practices will be discussed in detail to help those who want to build websites that are optimized, without having to compromise on the design or content.

Website development has come a long way – from a few simple lines of static HTML and drab layouts to dynamic pages with fluid and interactive designs. Websites are now a complex web of advanced HTML, intuitive code, heavy media content, images, and third-party plugins.

Inevitably, this has created bloated websites which directly affects the end user experience. The world of technology has risen to support modern websites with better hardware and browsers, but the average page speed of websites continues to inch upward. The growing number of sluggish websites has pushed the case for website optimization and the need for performance monitoring.

Why is Page Size a Metric?

Performance monitoring allows us to pinpoint where exactly a site is slowing down and what is causing it to do so. There are a number of metrics that help us gauge website performance, but one that directly influences the end user experience is the page size or the total downloaded bytes. The total page size can have a significant effect on the page speed, which is why minimizing webpage size is routinely cited as the first step in optimizing a website.

In this article, we will focus on data from the best ranked websites and the ones ranked lower to see exactly how much of an impact page size has on the overall page speed.

Impact of Page Size

The higher the number of elements/items on the page, the higher the number of connections needs to be established to download the content and consequently this adds to the overall load time. To understand this better, let us compare the data Catchpoint has collected for the top 50 IR websites as part of our upcoming Q2 Benchmark Report.

The table below lists the bottom 15 websites (ranked by Document Complete); we can see how the page size has a negative impact on the overall load time.

Now, let’s compare this data with the sites that ranked in the top 15:

There are two glaring conclusions to this comparison:

The website with the lowest total downloaded bytes (less than an MB) had an average of 102 items and a webpage response that was less than 2.3 seconds.

In contrast, the heaviest site (4.4 MB in total downloaded bytes) had an average of 283 items and a webpage response that is greater than six seconds.

Let’s view the effect of these numbers from a real user’s perspective using the Filmstrip feature–an important part of the Catchpoint monitoring tool.

Example 1 (Slow and heavy website)

Example 2 (Website with small page size)

The user has to wait 8 seconds to be able to fully load the website while the site with better performance loads within 3 seconds. The load time becomes more significant when you consider the fact that users expect websites to load within 2-3 seconds. This can be a pain for online retailers as impatient customers would quickly move on to a competitor’s website that loads much faster. The impact that page size has on load time cannot be ignored and the data we have compared makes it obvious – if we want to optimize site speed then we should first look at the page size and all the content that makes up the page.

Simply Static or Richly Dynamic?

Most businesses rely on their online presence for everything from branding, marketing to sales. It wouldn’t be fair to expect websites to use minimum images or content to improve speed, websites would not be able to cater to the growing demands of technology without the rich features and fluid design. We should instead focus on ways to trim the page size, to begin with – always follow the best practices. We will discuss, in detail, the techniques you must implement along with the best practices in the next post.