A fast, reliable way to put a number on usability
The SUS is a 10-question survey that gives you a single usability score you can track, compare, and defend. It's been validated across decades of research and it still holds up.
What the SUS Is
The System Usability Scale is a 10-question survey that produces a single usability score out of 100. It was created by John Brooke at Digital Equipment Corporation in 1986 and remains one of the most widely used usability measurement tools in the field. That longevity is a signal — it works.
The survey is technology-agnostic, quick to administer (under five minutes per participant), and doesn't require a specialist to interpret. You get a number you can track over time, benchmark against industry standards, and present to stakeholders without a lengthy explanation.
How to Administer It
After a {{LINK:usability-testing}} session or product interaction, ask participants to rate ten statements on a 1–5 Likert scale from "strongly disagree" to "strongly agree." The statements alternate between positive and negative framing:
- 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 support of a technical person to use this system.
- I found the various functions in this system were well integrated.
...and so on through ten items.
The alternating polarity forces respondents to engage with each statement rather than defaulting to a consistent rating pattern. The scoring is a small calculation: for odd items, subtract 1 from the score; for even items, subtract the score from 5; sum all results and multiply by 2.5.
How to Interpret the Score
The raw score lands between 0 and 100. Here's how to read it:
- 85+ — Excellent. Top-tier usability. Users find the product exceptional.
- 72–84 — Good. Above industry average. Minor friction remains but the experience is solid.
- 52–71 — Acceptable. Noticeably flawed. Users manage but aren't confident.
- Below 52 — Poor. Users are actively struggling. Significant redesign is likely needed.
The industry average across hundreds of published studies sits around 68. A score of 68 means your product is average — which is not the position you want to be in if UX quality is part of your value proposition.
SUS vs Other Usability Metrics
The SUS measures perceived usability — how users feel about ease of use. It doesn't directly measure task success rates, error rates, or time on task. Those are behavioural metrics captured through observation during usability sessions.
The SUS works best alongside behavioural data. A high task success rate paired with a low SUS score tells you users can complete tasks but feel like they're fighting the interface to do so. That's a very different problem to diagnose than a low task success rate.
Other perception-based scales like the UMUX offer similar value in less time, but the SUS has the largest body of benchmark data — which is what makes it genuinely useful for comparison across releases, products, and competitors.
Its Limitations
No single number captures the full picture. The SUS is a good overall signal but doesn't tell you where the usability problems are. Think of it as a temperature check, not a diagnosis.
It's also context-sensitive: the same product can receive meaningfully different SUS scores depending on the tasks participants completed before answering the survey. Always document the task context when reporting results.
Use it as part of a regular {{LINK:ux-benchmarking}} practice — tracked over time, across user segments, before and after major releases. That's where its value compounds.