The System Usability Scale (SUS) is a proven, internationally recognised method for measuring the usability of websites, apps and software. With just 10 statements, you get a score between 0 and 100 that you can compare against benchmarks from hundreds of studies. However, the classic SUS has two drawbacks: scoring is cumbersome, and it provides no qualitative feedback. Both are easy to fix. The result is the improved SUS 2.0. On this page, you’ll learn how the SUS is calculated, how to interpret the score and how to collect it with our free template.
Contents
How is the System Usability Score determined?
The original SUS questions are the following 10 statements:
- I think that I would like to use this website frequently.
- I found the website unnecessarily complex.
- I thought the website was easy to use.
- I think that I would need the support of a technical person to be able to use this website.
- I found the various functions in this website were well integrated.
- I thought there was too much inconsistency in this website.
- I would imagine that most people would learn to use this website very quickly.
- I found the website very cumbersome to use.
- I felt very confident using the website.
- I needed to learn a lot of things before I could get going with this system.
Respondents rate these statements on a five-point scale from “strongly agree” to “strongly disagree”. Points are awarded in the background, either from 0 to 4 or from 1 to 5.
Original SUS calculation: the SUS formula
As you can see from the SUS questions, every second statement is worded negatively. This means that a maximum score on question 1 means the exact opposite of a maximum score on question 2.
This makes the calculation very cumbersome. You subtract 5 from the sum of the points for the odd-numbered questions, then add 25 minus the sum of the points for the even-numbered questions. The result is multiplied by 2.5.
The SUS formula is:
(((1+3+5+7+9) - 5) + (25-(2+4+6+8+10))) * 2.5
A total of 100 points can therefore be reached if all odd-numbered questions receive the maximum score (strongly agree):
4 + 4 + 4 + 4 + 4 = 20
20 - 5 = 15
And all even-numbered questions are answered correspondingly positively (i.e. “strongly disagree”, the minimum score):
0 + 0 + 0 + 0 + 0 = 0
25 - 0 = 25
Applying the SUS formula gives:
15 + 25 = 40
40 * 2.5 = 100
This cumbersome calculation is necessary because a maximum score on one question means something different from a maximum score on another. “The app is very complicated” versus “The app is very easy to use”: here, “strongly agree” has the exact opposite meaning. One way round this would be to rephrase all statements negatively or all positively. But that, in turn, distorts the SUS.
We prefer a different approach:
The improved SUS 2.0
With LamaPoll, you can reverse the scoring. Positively worded statements stay at 0 to 4 points, while negatively worded statements are scored from 4 to 0.
An example of how points are awarded:
- If a participant strongly agrees with the statement “I can easily imagine using the app regularly”, 4 points are awarded.
- If a participant strongly agrees with the (negative) statement “I find the app unnecessarily complex”, 0 points are awarded.
SUS 2.0 questionnaire: in the questionnaire template at the bottom of this page, the points are already set up this way. Click “Use” to copy the questionnaire into your LamaPoll account and adapt it there as needed.
Calculating the SUS 2.0
The calculation is now far more intuitive and could hardly be simpler: you add up the responses and multiply the sum by 2.5:
Sum of the average scores for questions 1 to 10 × 2.5 = max. 100, min. 0
The SUS score is therefore calculated by adding up the average scores of the 10 items and multiplying the total by 2.5. As the maximum average score per item is 4, the 10 average scores add up to no more than 40 points. Multiplied by 2.5, this gives a best possible SUS score of 100.
A further advantage of the SUS 2.0
The System Usability Score is comparable to the original Net Promoter Score (NPS): easy to collect, but not enough on its own, because it lacks qualitative feedback.
We therefore recommend adding an input field to the SUS (as with the improved NPS). As long as the comment field is optional, it places no extra cognitive load on participants. Leaving a comment is entirely voluntary. In our experience, it is above all dissatisfied participants who appreciate the chance to give qualitative feedback. And criticism is far more valuable here than praise!
Example comment questions, depending on the product being evaluated:
- What should we change to make you happy?
- What did you like least?
- Which feature do you miss the most?
- What didn’t work?
- What was missing?
SUS 2.0 questionnaire template
The easiest way to measure usability is to survey users online. Feel free to use our free SUS 2.0 questionnaire template as a starting point, with the points already set up as described above. Click “Use” to copy the SUS questionnaire into your LamaPoll account and adapt it there as needed.
Worked example: one participant, two ways to calculate
A participant rates the 10 statements on a scale from 1 (strongly disagree) to 5 (strongly agree).
| Statement | Response (1 to 5) | SUS 2.0 points |
|---|---|---|
| 1 | 4 | 3 |
| 2 | 2 | 3 |
| 3 | 5 | 4 |
| 4 | 1 | 4 |
| 5 | 4 | 3 |
| 6 | 2 | 3 |
| 7 | 4 | 3 |
| 8 | 2 | 3 |
| 9 | 4 | 3 |
| 10 | 3 | 2 |
Original formula: odd-numbered statements 4 + 5 + 4 + 4 + 4 = 21, 21 − 5 = 16. Even-numbered statements 2 + 1 + 2 + 2 + 3 = 10, 25 − 10 = 15. (16 + 15) × 2.5 = 77.5
SUS 2.0: sum of the preset points 31, 31 × 2.5 = 77.5
Both methods give the same result. The SUS 2.0 simply saves you the conversion step.
Interpreting the SUS score: what counts as a good score?
The SUS score is not a percentage. A score of 68 doesn’t mean “68% good”, it means “average”: it is the mean across several hundred published studies. The grading scale by Sauro and Lewis shows how good a score really is:
| SUS score | Grade | Percentile |
|---|---|---|
| 84.1 to 100 | A+ | 96 to 100 |
| 80.8 to 84.0 | A | 90 to 95 |
| 78.9 to 80.7 | A− | 85 to 89 |
| 77.2 to 78.8 | B+ | 80 to 84 |
| 74.1 to 77.1 | B | 70 to 79 |
| 72.6 to 74.0 | B− | 65 to 69 |
| 71.1 to 72.5 | C+ | 60 to 64 |
| 65.0 to 71.0 | C | 41 to 59 |
| 62.7 to 64.9 | C− | 35 to 40 |
| 51.7 to 62.6 | D | 15 to 34 |
| 0 to 51.6 | F | 0 to 14 |
Source: Sauro & Lewis, Quantifying the User Experience (2016)
With a score of 77.5, the participant from the worked example falls into the B+ band, well above average. Because the SUS 2.0 only reverses how points are awarded, it produces exactly the same score as the original calculation, so the benchmarks still apply.
Using the SUS in practice
- Survey users straight after use, for example at the end of a usability test or after they complete a task, while the experience is still fresh.
- Keep the wording and order of the 10 statements and only swap “website” or “app” for your product. Otherwise your results are no longer comparable with the benchmarks.
- Ask participants to answer every statement. If they are unsure, they should pick the middle of the scale.
- Studies show the SUS delivers reliable results with as few as 12 to 14 participants (Tullis & Stetson, 2004). More participants make the score more precise.
- Repeat the survey regularly, for example after major releases, and compare the scores.
- Analyse the comment field. It shows exactly where the problems lie.
Conclusion: System Usability Scale
The SUS is a simple, low-cost benchmark. You don’t need external consultants to plan the methodology or objectives, or to carry out a complex implementation. The extended SUS also reveals a product’s specific weaknesses and makes the calculation far simpler.
What is LamaPoll?
LamaPoll is a survey tool for creating online questionnaires. Our survey tool lets you create, run and analyse online questionnaires quickly and easily. Create your questionnaire in just a few steps, customise it for your organisation and conveniently invite customers or employees by email. An online questionnaire enables you to gather insights quickly and easily to improve customer or employee satisfaction. You can register for the LamaPoll survey tool free of charge and immediately create and run online surveys with up to 50 participants. If you need more responses for your online questionnaire, simply choose one of our plans: billed monthly, cancel any month. You can also choose from our online questionnaire templates and examples.
