Having a site which is easy to use is one of the foundations of a successful website. In this article I will talk about how to audit your own website through usability testing to ascertain how usable it really is.

Before we do this, it would be a good idea to clarify what we mean by the term usability.

The definition of usability

The ISO 9241-11 definition of usability is as follows:

The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.

The key points to take from the definition above are effectiveness, efficiency and satisfaction and I will explain these more in a moment. Whilst the above is correct, I much prefer Steve Krug’s explanation of usability.

Usability really just means making sure that something works well: that a person of average (or even below average) ability and experience can use the thing – whether it’s a web site, remote control, or revolving door – for its intended purpose without getting hopelessly frustrated

How to measure website usability

There are a number of ways to measure the usability of a website. Usability testing, is a research method used to see how real people use your website and is one of the best ways to understand how your target audience actually uses your website.

The learnings from usability testing can be grouped and measured in the following ways.


Effectiveness can be measured by completing some usability testing and the moderator recording:

  • Whether or not a task was completed (thereby providing a completion rate for each task) irrespective of the route taken to complete the task.
  • How many times participants asked for/required assistance during a task (providing number of assists/prompts).


Efficiency can be measured by completing some usability testing and the moderator recording:

  • the time it takes the user to complete each task, and/or each step of the task
  • the participants response when asked whether the website enabled them to complete the task in an acceptable amount of time or not
  • whether the moderator felt the website enabled the participant to complete the task within an acceptable amount of time or not


Satisfaction can be measured by asking the participants of the usability testing to complete a brief questionnaire after they have finished performing the tasks.

Example Usability Findings

As detailed above, to achieve a reliable measure of usability, we need to measure the effectiveness, efficiency and satisfaction. One way to quickly analyse and report the findings of a usability test would be to grade each of these using a simple low, medium and high rating.

Here are four example usability test scenarios and their grading:

Example Scenarios

John wants to book the cheapest flight from London to Singapore on travelsite.com.

  • Scenario 1 – John books what he (wrongly) believes to be the cheapest flight in 5 minutes and leaves the website happy.
  • Scenario 2 – John succeeds in booking the cheapest flight, but it takes him 1 hour to do so. This is the first time John has booked online, and he leaves happy.
  • Scenario 3 – John suceeds in booking the cheapest flight in 10 minutes, but he leaves the site feeling that the site was hard to use.
  • Scenario 4 – John succeeds in booking the cheapest flight in 10 minutes and leaves the website feeling happy with his experience.

Example Results

In these scenarios I have given them what I feel is the applicable grade. Your gradings may differ slightly to mine as this type of measuring can subjective.

Scenario Effectiveness Efficiency Satisfaction
1 Low High High
2 High Low High
3 High Medium Low
4 High Medium High

Other Measurements

Other factors worth measuring usability could include:

  • Learnability – how easy is it for users to accomplish basic tasks the first time they encounter the design?
  • Memorability – when users return to the design after a period of not using it, how easily can they re-establish proficiency?
  • Errors – how many errors do users make, how severe are these errors, and how easily can they recover from the errors?
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