SUS Usability Score Online: The System Usability Scale
What Is SUS?
The System Usability Scale (SUS), proposed by Brooke in 1986, uses ten 5-point (1-5) items to quickly measure a product's usability, covering complexity, ease of use, consistency and confidence, with odd items worded positively and even items negatively. With few items and cross-product comparability, it is one of the most widely used standardized questionnaires in usability testing - testing with 5-10 users usually surfaces most usability problems.
How Scoring Works
Odd items (1, 3, 5, 7, 9) score = raw value minus 1; even items (2, 4, 6, 8, 10) score = 5 minus the raw value. Each item ranges 0-4, the 10-item total ranges 0-40, and multiplying by 2.5 yields the 0-100 SUS score. The tool applies this automatically, supports per-item entry or batch pasting of multiple questionnaires, and reports the mean SUS, standard deviation and odd/even consistency for cross-checking.
Interpreting the Result
The SUS score is on a 100-point scale but is not a percentage. Industry experience puts the average at about 68: above 68 usability is above average, below 68 needs improvement. Reference grades (Bangor et al.) are 85+ excellent (A), 70-84 good (B/C), 50-69 okay (D) and below 50 poor (F). The tool outputs the mean, grade band and benchmark comparison, and reminds you of the sample-size guidance (5-10 users usually finds the main problems).
How to Use It
After sign-in, enter each user's 10 raw item scores (one row per questionnaire); the tool computes the per-questionnaire SUS plus the overall mean, standard deviation and distribution, grade interpretation and benchmark comparison, and can export the details. Collect responses immediately after users finish core tasks, cover different user types, double-check suspicious questionnaires (all 5s or all 1s), and combine with interviews to understand the reasons behind the scores. Multi-round testing can track SUS trends to judge improvement.