What is the System Usability Scale (SUS)?
A standardized 10-question survey that measures perceived usability using a Likert scale. Created by John Brooke in 1986, SUS provides a quick, reliable way to evaluate any product, system, or interface.
Why Use SUS?
- Takes less than 2 minutes to complete
- Works for any product: websites, apps, hardware, software
- Produces a single score (0-100) that's easy to understand
- Scientifically validated with decades of research
- Free to use with no licensing restrictions
- Enables meaningful comparisons across products and studies
How to Run a SUS Survey
Have users complete a task
Let participants interact with your product or prototype. They should have enough experience to form an opinion.
Administer the questionnaire
Present all 10 SUS questions immediately after the task. You can create a free survey link to collect responses automatically, or use paper forms.
Calculate the score
Use our calculator or apply the scoring formula. Each response is adjusted, summed, and multiplied by 2.5 for a 0-100 score.
Interpret and compare
Compare your score against the industry average (68) and use the adjective ratings to communicate results to stakeholders.
The 10 SUS Questions
Questions alternate between positive and negative statements to reduce response bias. Each is rated on a 5-point Likert scale from “Strongly Disagree” to “Strongly Agree.”
- 1I think that I would like to use this system frequently.
- 2I found the system unnecessarily complex.
- 3I thought the system was easy to use.
- 4I think that I would need the support of a technical person to use this system.
- 5I found the various functions in this system were well integrated.
- 6I thought there was too much inconsistency in this system.
- 7I would imagine that most people would learn to use this system very quickly.
- 8I found the system very cumbersome to use.
- 9I felt very confident using the system.
- 10I needed to learn a lot of things before I could get going with this system.
Positive·Negative
How Scoring Works
The formula normalizes responses to a 0-100 scale, accounting for the alternating positive and negative questions.
Score = Response - 1
Score = 5 - Response
Example
Sum all adjusted scores (0-4 each), then multiply by 2.5.
Score Interpretation
The industry average is 68. Scores are graded on a curve based on research by Bangor, Kortum, and Miller.
| Score | Grade | Rating |
|---|---|---|
| 90-100 | A+ | Best Imaginable |
| 85-90 | A | Excellent |
| 72-85 | B | Good |
| 52-72 | C | OK |
| 38-52 | D | Poor |
| 0-38 | F | Awful |
Frequently Asked Questions
What is a good SUS score?
A score above 68 (the industry average) is considered above average. Scores above 80 are considered good, and above 90 is excellent. However, what's "good" depends on your context and goals.
How many responses do I need?
You can get useful insights with as few as 5 responses, but 12-14 is recommended for more reliable results. For statistical confidence, aim for 20+ responses.
Can I modify the questions?
You can replace the word "system" with your product name, but the 10 questions themselves should not be modified. The validity of SUS depends on using the standardized questionnaire.
When should I administer SUS?
Immediately after users have interacted with your product. SUS measures perceived usability, so users need recent experience to provide accurate ratings.
Is SUS score a percentage?
No. A score of 70 doesn't mean "70% usable." SUS scores are normalized values meant for comparison against benchmarks and other products, not absolute percentages.
Ready to measure usability?
Use our free calculator to get your SUS score in under 2 minutes.
References
- Brooke, J. (1996). “SUS: A quick and dirty usability scale.” Usability Evaluation in Industry.
- Bangor, A., Kortum, P., & Miller, J. (2009). “Determining What Individual SUS Scores Mean.” Journal of Usability Studies.