SUS Usability Scale – How to use it to improve your UX?

A usability scale is an evaluation tool to quantify the usability of a product, website or app. These scales are commonly used in UX design to obtain an assessment of how users interact with the product. Among the usability scales, the best known is the System Usability Scale. Today we tell you how to use it to evaluate the usability of your designs.

What is the SUS usability scale?

The SUS usability scale (System Usability Scale) is a standard and simple method to measure the usability of a product. Once users have interacted with the system being evaluated, they are invited to fill in a simple UX survey with a questionnaire composed of 10 sentences with which they have to rate their degree of agreement:

• I think I would like to use this system frequently.
• I found the system unnecessarily complex.
• I thought the system was easy to use.
• I think I would need the help of an expert to use this system.
• I found the different functions of the system to be well integrated.
• I thought there was too much inconsistency in the system.
• I imagine that most people would learn to use this system quickly.
• I found the system very cumbersome to use.
• I felt confident using the system.
• I would need to learn a lot of things before I could use the system properly.

The degree of agreement is measured on a Likert scale from 1 to 5, with 1 being ‘strongly disagree’ and 5 being ‘strongly agree’.

• 1: Strongly disagree
• 2: Disagree
• 3: Neutral
• 4: Agree
• 5: Strongly Agree

The SUS scale score is calculated as follows;

• For odd statements (1, 3, 5, 7, 9): Subtract 1 from the score given by the user.
• For even statements (2, 4, 6, 8, 10): Subtract the score given to the user from 5.
• Add all values together. The total must be between 0 and 40.
• Multiply the total sum by 2.5 to get a usability score on a scale from 0 to 100.

The rule developed by Jeff Sauro, who built a large database of SUS usability scale surveys, is used to interpret the results:

• Between 80 and 100: excellent usability.
• Between 68 and 80: better than average usability.
• Between 50 and 68: poor usability.
• Between 0 and 50: the system has significant usability problems.

SUS usability scale with We are testers

Organising a UX survey to determine the SUS usability scale value is easy with We are testers. The usability scale questionnaire is easily entered into our research platform to create the survey. Through our panel of consumers and users we can select the sample that most closely matches your target audience and create a list of tasks for them to consistently interact with the system. After they complete the tasks, they are submitted to the questionnaire and you get the answers quickly. Then you just have to calculate the value of your SUS and compare it to the standard.

Interested in improving your UX designs? Ask our experts how the SUS usability scale and other usability tests can help you improve the experience.