“Is our product easy to use?” It sounds like a simple question, yet teams often answer it with opinions, anecdotes or a handful of support tickets. Stakeholders want a number, designers want insight, and everyone wants to know whether the latest redesign actually helped.

The System Usability Scale (SUS) gives teams a quick, reliable way to put a number on perceived usability. This guide explains what SUS is, how to run it, how to calculate and interpret scores, and how to use it well.

What Is the System Usability Scale?

The System Usability Scale is a standardized questionnaire that measures how users perceive the usability of a product, website, app or system. It was created by John Brooke in 1986 as a “quick and dirty” tool, and it has since become one of the most widely used usability measures in the industry.

SUS consists of 10 statements, each rated on a 5-point scale from “Strongly disagree” to “Strongly agree.” Responses are converted into a single score from 0 to 100.

Its popularity comes from several strengths:

• Simple and fast, taking about two minutes to complete
• Technology-agnostic, working for websites, mobile apps, software, hardware and even voice interfaces
• Reliable, even with small samples
• Free to use with proper attribution
• Benchmarkable, since decades of data exist for comparison

What SUS Measures (and What It Doesn’t)

SUS captures perceived usability: how easy, consistent and confidence-inspiring users find a system overall. It gives a high-level view of the experience rather than a diagnosis.

It does not tell you why a score is high or low, which screens cause problems, or what to fix. Think of it as a thermometer, not an X-ray. It tells you whether something is wrong and how things change over time, and other methods help you find the cause.

The 10 SUS Statements

Participants rate each statement from 1 (strongly disagree) to 5 (strongly agree):

1. I think that I would like to use this system frequently.
2. I found the system unnecessarily complex.
3. I thought the system was easy to use.
4. I think that I would need the support of a technical person to be able to use this system.
5. I found the various functions in this system were well integrated.
6. I thought there was too much inconsistency in this system.
7. I would imagine that most people would learn to use this system very quickly.
8. I found the system very cumbersome to use.
9. I felt very confident using the system.
10. I needed to learn a lot of things before I could get going with this system.

Notice the alternating tone: odd-numbered items are positive, even-numbered items are negative. This design reduces response bias, because participants must read each statement rather than tick the same column all the way down. In practice, replace “system” with the name of your product, such as “app” or “website,” and keep the rest of the wording intact.

How to Calculate a SUS Score

Scoring takes a few steps:

1. For odd-numbered items (1, 3, 5, 7, 9): subtract 1 from the response.
2. For even-numbered items (2, 4, 6, 8, 10): subtract the response from 5.
3. Add up all ten adjusted values (each now ranges from 0 to 4).
4. Multiply the total by 2.5 to get a score from 0 to 100.
5. Average the scores across all participants.

Quick example: Suppose a participant answers 4, 2, 4, 1, 5, 2, 4, 2, 4, 2.

• Odd items: (4-1) + (4-1) + (5-1) + (4-1) + (4-1) = 3 + 3 + 4 + 3 + 3 = 16
• Even items: (5-2) + (5-1) + (5-2) + (5-2) + (5-2) = 3 + 4 + 3 + 3 + 3 = 16
• Total = 32, and 32 × 2.5 = 80

An important caution: the result is a score, not a percentage. A SUS of 70 does not mean “70% usable.”

How to Interpret SUS Scores

Research across thousands of studies has found an average SUS score of roughly 68. That figure is the most useful reference point:

• Above 68: better than average
• Around 68: average usability
• Below 68: below average, with room to improve

Many teams also use letter-grade or adjective bands as a rough guide:

Treat these bands as guidelines. A “good” score for a complex enterprise tool may differ from a consumer app, so compare against similar products and, above all, against your own previous results.

When to Use SUS

SUS fits many situations:

• After usability testing sessions, to capture participants’ overall impression
• Before and after a redesign, to measure whether the experience improved
• Benchmarking against competitors or industry averages
• Tracking usability across releases as part of ongoing UX metrics
• Comparing design alternatives when you need a single comparable number
• Reporting to stakeholders who prefer simple, trackable metrics

It is less useful when you need to diagnose specific issues or assess a single feature in isolation, since it evaluates the overall system.

How to Run a SUS Survey

Step 1: Define the scope

Decide exactly what you are measuring: the whole product, a specific module or a prototype. Participants should understand what “the system” refers to.

Step 2: Choose participants who have used the product

SUS works best after real experience with the product, either a task-based test or genuine prior use. Asking people who have never touched it produces unreliable results. Recruit participants who reflect your actual audience, guided by your user personas.

Step 3: Administer it at the right moment

In a usability test, give the questionnaire immediately after the tasks, before discussion, so impressions are fresh and not influenced by conversation. For live products, trigger surveys after meaningful use rather than at first login.

Step 4: Keep it clean

Don’t change the wording, reorder statements or remove items, since this undermines comparability. Ask participants to respond instinctively rather than overthinking each statement.

Step 5: Gather enough responses

Reasonably stable scores can emerge from as few as 8 to 12 participants, though larger samples (20 or more) give more confidence, especially when comparing versions or segments.

Step 6: Score, analyze and report

Calculate individual and average scores, and report a confidence interval if possible. Pair the number with qualitative observations to explain it.

Best Practices for Using SUS Effectively

1. Pair SUS with qualitative research

A score is only the beginning. Combine it with observation, interviews and task analysis to uncover the reasons behind it. Our overview of UX research methods shows how to choose complementary techniques.

2. Use it as a trend, not a one-off

A single score has limited meaning. Measure at regular intervals, such as every quarter or major release, and track movement. A rise from 62 to 74 after a redesign tells a clear story.

3. Benchmark against comparable products

Compare against competitors or industry norms where available, and against your own history. Context turns a number into insight.

4. Segment your results

Break scores down by user type, experience level or platform. New users might rate a product much lower than experienced ones, revealing onboarding problems that an overall average hides.

5. Connect to heuristics and audits

When scores are low, use structured evaluation to find causes. A review against usability heuristics helps pinpoint issues that drag perceived usability down.

6. Build SUS into your testing process

Include it as a standard step in usability studies so scores accumulate over time. Our usability testing and feedback loops service shows how to make measurement part of a continuous improvement cycle.

7. Communicate results clearly

Present the score with context: the sample size, the comparison point and what it means for the roadmap. Avoid over-claiming precision from small differences.

Common Mistakes to Avoid

• Treating the score as a percentage
• Modifying the statements and then comparing to standard benchmarks
• Surveying people who haven’t used the product
• Drawing conclusions from tiny differences without checking statistical significance
• Using SUS alone to decide what to fix
• Ignoring segments, which can mask serious problems
• Collecting scores without acting on them

Alternatives and Companions

SUS is not the only metric. Teams often pair it with the Net Promoter Score (loyalty), Customer Satisfaction (CSAT), the Single Ease Question (task-level difficulty), task success rates and time on task. Each answers a different question, and together they give a balanced view of the experience.

Bringing It All Together

The System Usability Scale is a simple, proven way to turn usability perception into a number you can track, compare and communicate. With just ten questions, it helps teams see whether their efforts are making the product easier to use and where they stand against an industry average of about 68.

Use it consistently, keep the wording intact, combine it with qualitative insight and focus on trends over time. Used this way, SUS becomes a dependable compass for design decisions.

If you want help measuring and improving the usability of your product, work with a trusted UI UX design company in Bangalore that can help you research, test and refine experiences users find genuinely easy to use.