How to measure your sites speed

“Asking users to wait is like asking them to leave”

A slow website creates a poor experience. Users with a broadband connection expect websites to deliver instant information, and asking users to wait is like asking them to leave.

A fast website encourages people to keep using the site you spent weeks or months creating for them.

Is your website fast or slow?

In this paper we introduce straightforward techniques for measuring the speed of your site’s web pages using a Windows-based PC. We give recommendations for page load goals and help with diagnosing the cause of slow web pages.

How do you measure page load times? Two common mistakes  

The only meaningful measurement of a page’s speed is “how fast a page loads in a customer’s web browser”. Because there is no way to measure the speed of an entire site, you should measure the speed one page at a time. The homepage is a good place to start.

“Measure page load time, not server processing time”

There are two common mistakes people make when measuring page load times:

  • Mistake 1: Measuring server processing time.
    The time it takes for a web server to process and produce is usually only 10-20% of the page load time. To measure page load times you need to make the measurement using a web browser.
  • Mistake 2: Assuming customers have the same load times as you do.
    If you’re a developer or operations engineer, you probably have a faster page load time than your customers, either because you’re located physically closer to the web server, or because you access the web the server through a faster or same-segment connection. Your users will have higher network latency caused by distance and/or a slower network connection to the web server.

The only accurate measurement is to measure how long the user’s browser takes to load a page from their location.

How long should your customers wait?

“Thirty-three percent of consumers shopping via a broadband connection will wait no more than four seconds for a Web page to render”

There is growing research to connect slow page load times with low customer satisfaction and high site abandonment.  For happy customers, set page load goals, measure against these goals and take action where necessary. The following recommendations are based on accredited industry research, and are for an average user with a regular Windows-based PC, 1Mb broadband connection and Microsoft Internet Explorer or Mozilla Firefox.
Page load goal: 4 seconds
Based on research from Jupiter and Akamai[1], “Thirty-three percent of consumers shopping via a broadband connection will wait no more than four seconds for a Web page to render”. For page load times, four seconds is the current goal to aim for.
Page load upper maximum: 8 seconds
The “8 second rule” was proposed by Zona Research[2] in 1999. A decade ago in the days of pre-Pentium computers and dial-up, this was an admirable standard to achieve; today it should serve as a maximum wait time after which people will leave wondering if the site is broken.
Exceptions: warm-load and processing pages
The two exceptions are warm-load (when someone navigates back to a previous page – these pages need to load in under two seconds. Processing pages such as credit card validation or signing in can take longer – people expect to wait if they perceive the website is doing some work requested on their behalf.
Based on these, we recommend the following goals for an average user with a broadband connection:

Page type A: Great B: Fair C: Bad
First time visit (no cache) < 4 seconds 4 – 8 seconds > 8 seconds
Warm load (primed cache) < 2 seconds 2 – 8 seconds > 8 seconds
Processing page < 4 seconds 4 – 15 seconds >15 seconds

Measure your site’s speed

The only meaningful measurement of a page’s speed is how fast a page loads in a customer’s web browser from their location – network latency plays a huge role in page load times, and measuring speed from a PC located close to the web server does not capture the real-world travel time over the internet.

We recommend using one of two methods for measuring a page’s speed:

a) If the page is an internet-facing public page, use the AOL Page Test to measure page load times from Dulles, VA, USA. This is a free website where you enter your site’s URL, and the server loads the page with Internet Explorer and displays the results after a few seconds.

If the page is an intranet or non-public internet page, use either Microsoft Internet Explorer or Mozilla Firefox to measure the local page load time and apply a multiplier to estimate the load time for users accessing the site remotely.

Before we start, let’s familiarize ourselves with the Waterfall diagram (shown right). This is a standard diagram produced by performance measuring tools.

The Y axis shows the files (requests) in the order they were loaded. The X axis shows elapsed time.

In the image to the right, the HTML page for is loaded first, then the CSS files, JavaScript files and images. The HTML, JavaScript and CSS files are loaded sequentially one-after-the-other, while several images are loaded in parallel.


Server-based testing: AOL PageTest

The AOL PageTest is a free over-the-web tool for performance testing a page from Dulles, VA, USA.

To use the AOL PageTest:

1. Go to

2. Type in your site address, e.g., then click the Submit button.

3. The page will refresh a few times then show you the cold and warm load times for the page with a waterfall diagram.

The AOL page test is more accurate than most web-based tools a real browser to measure load times – many other web-based tools approximate load times by parsing HTML files.


Client based testing: httpWatch and Firebug

Neither Microsoft Internet Explorer or Mozilla Firefox have capabilities for measuring a page’s speed, but there are add-ons available for each that produce waterfall diagrams and page load diagrams. We recommend using either tool to measure page load times from a client:

Microsoft Internet Explorer versions 6,7 or 8
httpWatch is an affordable extension for Internet Explorer that gives page load timings and analysis of requests, available from

Mozilla Firefox versions 2,3
Firebug is a free extension for Firefox that gives page load timings and a number of development capabilities, available from

clip_image002[10] clip_image002[12]

Because these tools give you the timings from your local machine, you need to apply a multiplier to estimate the effect of network latency for remote users:

1. Use Microsoft Internet Explorer with httpWatch or Mozilla Firefox with Firebug to measure the page load time from “onsite” – a workstation physically close to the web server. This is your local page load time.

2. Apply the following formula to estimate the effect of network latency for a user located with a 1Mb connection located within 1,000 miles of the server:


For example, suppose you have a 0.5 second local load time, and the page has 20 requests and is 350KB in size, the page load time would be:


this equals 3.439394 seconds.

Analyze your page load time

If your page load time doesn’t meet an acceptable goal, you can quickly make an analysis using the page load waterfall diagram.

Page load time is governed by:

· Backend processing. The time it takes for a server to process the page, produce the HTML and resources and return the HTML to the browser.

Frontend processing. The time it takes for the browser to render the HTML and load the page resources – JavaScript, CSS, and images.


If the HTML page takes a long time to process, tuning the application, optimizing database queries and adding hardware will improve the page load time. If the JavaScript, CSS, image resources take a long time to load, applying frontend optimization techniques will reduce the page load time.

Typically, backend processing contributes 10% to the page load time, and frontend processing contributes 90% to page load time.

If you need to tune frontend processing, look at the Runtime Page Optimizer – a software component that automates many of Yahoo’s “best practices for speeding up websites”, increasing the speed a page loads by combining, compressing and caching JavaScript, CSS and images. Now available for ASP.NET and SharePoint sites. See for more information.





This article is brought to you by the fantastic people at RPO.


Popular Posts