System Usability Scale (SUS)
A 10-question survey that gives a usability score from 0 to 100.
SUS = (sum of odd items − 5 + 25 − sum of even items) × 2.5
Why it matters
It is quick, free and widely used, so you can compare across products and over time.
How to use it
- Give it right after people use the product.
- Use the exact wording of the questions.
- Compare with the commonly cited average of about 68.
Example
A score of 80 is well above average. A score of 50 suggests serious problems.
Watch out
The score is not a percentage, and it tells you how usable a product feels, not what to fix.