System Usability Scale for measuring usability

The System Usability Scale (SUS) is a questionnaire that measures the usability or usability of a website or app, taking into account the context in which the product is used. You can read more about usability and usability testing in this article: what is usability testing?

In this article you will find out where the system usability scale comes from, we explain how to interpret the results and we provide you with the Dutch translation of the system usability scale questionnaire. 

Where does the System Usability Scale (SUS) come from?

The System Usability Scale was developed and put into use well before the breakthrough of the internet. In 1986 John Brooke developed the questionnaire and more than 30 years later it is still widely used. 

Before developing the System Usability Scale, John Brooke determined that measuring the usability of a product is not an exact science as it largely depends on the context in which the product is used. Something that still makes sense in today's environment.

What was missing at the time was an efficient tool to gain insight into the user-friendliness of your own system, but at the same time also be able to compare it with other systems in the market.

That gap was filled by the System Usability Scale. A questionnaire with ten questions in which the usability of a product is measured, but taking into account the context in which the product is used.

This made it possible to measure usability in a uniform manner and compare it with other products, companies and industries. Very handy!

Biggest advantages of the System Usability Scale questionnaire are:

  • Uniform output and benchmark. The main advantage is that the SUS expresses usability on a scale from 1 to 100, allowing you to compare results against other products, the competition or the industry average.
  • Reliable results. The System Usability Scale has been tested several times and provides reliable results, even with smaller samples.
  • Quick overview of usability. Because the SUS questionnaire only consists of ten questions, it takes little time to complete it and you quickly have an indication of its usability.

2 - The System Usability Scale Questionnaire (Dutch)
Respondents are asked to rate the ten statements below using the Likert scale. There are five answer options here, ranging from completely disagree to completely agree.

Below you will find the ten questions of the SUS questionnaire:

  1. Ik denk dat ik dit product frequent zou willen gebruiken. 
  2. Ik vond het onnodig ingewikkeld. 
  3. Ik vond het product makkelijk te gebruiken. 
  4. Ik denk dat ik technische support nodig heb om het product te gebruiken. 
  5. Ik vond de verschillende functies van het product goed met elkaar geïntegreerd. 
  6. Ik vond dat er te veel tegenstrijdigheden in het product zaten.
  7. Ik kan me voorstellen dat de meeste mensen snel met het product overweg kunnen. 
  8. Ik vond het product omslachtig in gebruik. 
  9. Ik voelde me zelfverzekerd tijdens het gebruik van het product. 
  10. Ik moest veel over het product leren voordat ik het goed kon gebruiken.

3 - Calculate SUS Score
Follow the steps below to calculate the SUS Score. Take into account the points associated with each answer:

Totally disagree
1 point - Completely Disagree
2 points - Disagree
3 points - Neutral
4 points - Agree
5 points - Totally agree

Step 1 - Calculate Odd Number Score - (X-1)
The first step is to calculate the score for all odd numbers. You do this by looking at the number of points scored and subtracting 1 point (X-1).

Example: When someone answers "Agree" to the first question, it is worth four points (X = 4, see table). From this you get a point, making the score for that question 3 points (X-1).

Step 2 - Calculate score even numbers - (5 - X)
The second step is to calculate the score for all even numbers. You do this by looking at the number of points scored and subtracting it from 5 (5-X).

Example: When someone disagrees with the first question, it is worth two points (X = 2, see table). Then you subtract two from five, making the score for that question 3 points (5-X).

Step 3 - Calculate the SUS Score - (Score step 1 + score step 2) * 2.5
In this step you add all points from steps 1 and 2 together. You then multiply the total score by 2.5. The answer you get is the SUS score!

Example: Assume the total number of points from step 1 is 15 (3 + 4 + 2 + 4 + 2 = 15). And in step 2 10 (2 + 4 + 3+ 1 + 0 = 10). Add 15 and 10 together to get 25 points. You multiply this by 2.5 (15 + 10) * 2.5 = 62.5. The SUS score is then 62.5.

4 - Interpreting the results
If you have calculated the SUS score using the above method, you get a score (no percentage!) Between 1 and 100. In addition, a score of more than 80.3 means that you are in the top 10%, a score of above 68 in the top 30% and from 68 in the top 50%.

80.3 or above - Excellent
68 - 80.3 - Good
68 - OK
51 - 68 - Below Average
51 or below - Poor

Alt text: meaning system usability score