--- title: "System Usability Scale" url: "https://www.insideuxdesign.com/en/glossar/system-usability-scale" language: "en" description: "What is the System Usability Scale? A plain-language guide with scoring, an example and practical tips. Learn how to read and compare SUS scores correctly." published: "2026-10-14T09:50:32+02:00" updated: "2026-10-14T13:02:27+02:00" --- # System Usability Scale The System Usability Scale (SUS) is a short, standardized questionnaire with ten statements. It sums up how usable people perceive a product to be as a single score from 0 to 100. - **Buchstabe:** S UX glossary # System Usability Scale The System Usability Scale (SUS) is a short, standardized questionnaire with ten statements. It sums up how usable people perceive a product to be as a single score from 0 to 100. Imagine a team that has just redesigned the customer portal of an energy provider. The tests went well, but management wants a number: is the new portal really easier to use than the old one? That’s exactly the kind of question the System Usability Scale, or SUS, is built for. ## Explained simply The SUS is a questionnaire with ten statements that participants fill out right after using a product. For each statement, they rate how much they agree on a scale from 1 (“strongly disagree”) to 5 (“strongly agree”). One of the statements reads: “I found the system unnecessarily complex.” The result is a single score between 0 and 100. Think of it like the star rating after a taxi ride. It quickly tells you how satisfied someone was overall, but not whether it was the driving, the route or the music. John Brooke created the questionnaire in 1986 at the computer company Digital Equipment Corporation (DEC). He himself calls it “quick and dirty,” a fast and deliberately simple tool. ## How to calculate the score The odd-numbered statements are worded positively, the even-numbered ones negatively. For odd items, subtract 1 from the response. For even items, subtract the response from 5. Add up the ten results and multiply the total by 2.5. That’s your SUS score. A simple spreadsheet is all you need. One important point: the score is not a percentage. Jeff Sauro of MeasuringU analyzed data from around 500 studies and found an average of 68. So a score of 68 is middle of the road, not “68 percent good.” Scores above roughly 80 put you in the top ten percent. ## An example Back to the energy provider. Before: the old portal gets an average SUS score of 58 from twelve participants, which is below average. After: once the redesign is done, twelve different participants complete the same tasks and the same questionnaire, and the new portal scores 77. The team can now show that perceived usability has clearly improved. Which spots still caused trouble, though, only becomes visible through the observations from [usability testing](https://www.insideuxdesign.com/en/glossar/usability-testing). ## Common misconceptions The SUS is not a diagnostic tool. Brooke himself stresses that the individual statements aren’t meant to pinpoint specific problems. For that, you need observation or a [heuristic evaluation](https://www.insideuxdesign.com/en/glossar/heuristic-evaluation). To learn more about what usability actually means, read [What Is Usability?](https://www.insideuxdesign.com/en/blog/what-is-usability). ## In practice - **Ask right after the test.** Have people fill out the questionnaire before you discuss the tasks. Otherwise, the conversation colors their answers. - **Keep changes to the wording minimal.** The benchmarks come from studies using the established wording. The more you rephrase, the less you can compare your scores against them. - **Compare instead of celebrating single scores.** The SUS becomes meaningful in comparison: old version against new, or your product against the average. ## Related terms [Usability Testing](https://www.insideuxdesign.com/en/glossar/usability-testing), [Heuristic Evaluation](https://www.insideuxdesign.com/en/glossar/heuristic-evaluation), [User Research](https://www.insideuxdesign.com/en/glossar/user-research) ## Sources - [John Brooke: SUS: A Retrospective. Journal of Usability Studies, 2013](https://uxpa.org/jus/sus-a-retrospective/) - [Jeff Sauro: Measuring Usability with the System Usability Scale (SUS). MeasuringU, 2011](https://measuringu.com/sus/) ## More terms [ ### A/B Testing An A/B test is an experiment that shows two versions of a page or element at the same time to randomly split groups of visitors. It lets you decide with real data which version works better. ](https://www.insideuxdesign.com/en/glossar/a-b-testing) [ ### ARIA ARIA is a W3C standard that adds roles, states and properties to HTML. It tells screen readers what an element is and how it currently behaves. ](https://www.insideuxdesign.com/en/glossar/aria) [ ### Accessibility Accessibility means designing websites, apps and digital documents so that everyone can use them, including people with visual, hearing, motor or cognitive disabilities. ](https://www.insideuxdesign.com/en/glossar/accessibility) [ ### Affordance An affordance describes what action an object makes possible and whether people can recognize it: a button invites you to press it, a handle invites you to pull. ](https://www.insideuxdesign.com/en/glossar/affordance) [ ### Alt Text Alt text is a short text version of an image, stored in the HTML alt attribute. Screen readers read it aloud so people who can’t see the image get the same information. ](https://www.insideuxdesign.com/en/glossar/alt-text) [ ### Atomic Design Atomic Design is a method for building user interfaces from small, reusable building blocks, from single elements like buttons all the way up to complete pages. ](https://www.insideuxdesign.com/en/glossar/atomic-design) [ ### BFSG The BFSG, Germany’s Accessibility Strengthening Act, has required many companies since 28 June 2025 to make certain products and digital services, such as online shops, accessible. ](https://www.insideuxdesign.com/en/glossar/bfsg) [ ### Card Sorting Card sorting is a research method in which people sort terms written on cards into groups. It shows you how they mentally organize content, so you can plan navigation that makes sense to them. ](https://www.insideuxdesign.com/en/glossar/card-sorting) [ ### Cognitive Load Cognitive load is the mental effort it takes to understand and use an interface. The less unnecessary thinking a design demands, the easier the actual task becomes. ](https://www.insideuxdesign.com/en/glossar/cognitive-load) [ ### Color Vision Deficiency A color vision deficiency means someone has a harder time telling certain colors apart than most people. The most common type is red-green deficiency. ](https://www.insideuxdesign.com/en/glossar/color-vision-deficiency) [ ### Contextual Inquiry Contextual inquiry is a research method where you observe and interview people in their real work environment. It shows you how they actually get tasks done, not just how they describe it. ](https://www.insideuxdesign.com/en/glossar/contextual-inquiry) [ ### Contrast Ratio The contrast ratio describes how much two colors differ in brightness, such as text and background. WCAG requires at least 4.5:1 for normal text. ](https://www.insideuxdesign.com/en/glossar/contrast-ratio)