System Usability Scale 101 — An extensive insight in quantitative usability

TL;DR: SUS is a very reliable measurement of a system’s perceived usability. It uses 10 questions, graded from strongly disagree to strongly agree, to measure perceived usability. With a sample size of 12 the results have an accuracy of 100%.

A big amount of effort is attributed to uncovering usability issues of a system. System Usability Scale is a quantitative measure of the usability of the system. Although it doesn’t pinpoint specific attributes [of the system] that affect usability, it is shown to be one of the most powerful ways to put a number on the system’s perceived usability [1].

Purpose of this document is to provide an extensive insight in the current state of the System Usability Scale, with the most recent information. Updated regularly.

Setting up the System Usability Scale (SUS)

The SUS is a questionnaire that can be administered either verbally in a moderated environment, or written in an unmoderated environment. It was initially introduced in 1986 by John Brooke as an undimentional, quick-and-dirty way of measuring usability [2] and was validated numerous times [3, 4]

The questions of the SUS

The SUS consists of 10 questions, interchanging positive and negative wordings. Following are the original questions with the number 8 modified by Finstad for non-native english speakers [5]

  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/awkward 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.

The responses of the SUS

Each question is supposed to be answered on a scale from 1 (Strongly Disagree) to 5 (Strongly Agree) [2]. Participants shouldn’t dwell into any specific questions, but instead respond with their first thoughts. If the test is administered verbally and the participant doesn’t answer a specific question, it is scored as a 3.

Sample SUS –

Calculating the score of SUS

The rules:

  • Each question’s score ranges between 0 and 4
  • Positively worded questions are 1, 3, 5, 7 and 9
  • Negatively worded questions are 2, 4, 6, 8 and 10

Scoring each question:

  1. For positively worded questions take the number of the answer and subtract 1 (e.g. if the answer of the question one was neutral — 3, then the score of the question one is 3 – 1 = 2)
  2. For negatively worded questions take the number of the answer and subtract it from 5 (e.g. if the answer of he question two was agree — 4, then the score of the question two is 5 – 4 = 1)

After that, the overall score of the SUS is calculated as follows:

  1. Add all 10 questions’ scores
  2. Multiply the number by 2.5
  3. You will get a number between 0 and 100, which is the SUS score

If you want to save the manual work, you can just enter the scores of each question for up to 150 participants and get all relevant results in our free SUS calculator.

Extracting learnability measurements

Although there was some evidence by James R. Lewis and Jeff Sauro that SUS measures two dimensions of one’s system: Learnability and Usability [6], this is not considered the case in most studies. Instead Lewis and Sauro reviewed 9000 questionnaires to find a factorisation of negatively vs positively worded questions rather Usability and Learnability [8]. However, there is some connection between the questions 4 and 10 that in some cases may be strong enough to form a separate factor [8].

If it is proven than in the specific field of the study (most of the time not the case), questions 4 and 10 form a separate factor (specifically measure learnability), the SUS’s learnability score can be extracted as following:

  1. Add the scores of questions 4 and 10
  2. Multiply the result by 12.5
  3. You will get a number between 0 and 100, which corresponds to the learnability of the system

Understanding the score of SUS

A score of 0 translates to “it is impossible to perform the required task”, whereas a score of 100 means that the required task is performed easily. However, most systems are evaluated by testing a flow with numerous tasks; thus realistically it is very difficult for a score to be close to 0 [4]. In general, it is suggested to use the System Usability Score as a relative measurement to the system tested. A system with higher SUS as another means that is more usable, although how much more usable is not up for the SUS to show.

The Bangor et. al scale for SUS scores. Score less than 25 is considered "worst imaginable", around 38 "poor", around 52 "OK", around 72 "Excellent", around 98 "Best imaginable".

Comparing the score

Nonetheless, it comes in handy to understand how the system in question performs to other real software, instead of just looking at the theoretical classification. The average of the SUS score from approximately 500 products, with a varied categorisation, is 68.

How many participants should be included in a SUS test

The power of SUS is also shown in the sample size needed to achieve statistical significance. Thomas S. Tullis and Jacqueline N. Stetson showed that from 12 participants and more the SUS result remains the same [1].

Image courtesy of Thomas S. Tullis and Jacqueline N. Stetson

Can you change the word “system” in the SUS questions?

SUS is quite resilient to changes in the name of the “system”. Bangor et al. changed the word “system” with “product” and didn’t see a significant change in the results [3]. This suggests that probably other, more specific, synonyms of “system” could be used safely.

Internationalised SUS vs non-native English speakers

The SUS is tested with non-native English speakers and its reliability stays the same. However several researchers have translated and validated SUS into local languages. If the participants are native speakers of a language other than English, it is worth considering using the local version of the SUS.

Does perceived Usability affect loyalty?

There exists initial data to support a link between the perceived usability of a system and users’ loyalty. Users who are promoters, measured with NPS, rate the system with substantially higher usability than passives and detractors. That could potentially indicate that improving usability could increase the likelihood of a user becoming a promoter.

What about the positive SUS?

Sauro and Lewis developed an all-positively worded version of the System Usability Scale. It performs as well and is as reliable as the original SUS.

Validated translations of the System Usability Scale

The Chinese System Usability Scale

  1. 我愿意经常使用这个系统.
  2. 我发现这个系统太复杂.
  3. 我认为这个系统使用起来很容易.
  4. 我认为我需要技术人员的帮助才能使用这个系统.
  5. 我发现这个系统很好地集成了各种功能.
  6. 在使用该系统的过程中, 我发现很多操作结果和预想功能不一致.
  7. 我想大多数用户能很快学会使用该系统.
  8. 我发现这个系统使用起来很别扭.
  9. 我对熟练掌握这个系统很有信心.
  10. 在使用这个系统之前, 我需要学习很多知识.

Adaption by Yuhui Wang, Tian Lei & Xinxiong Liu

The Danish System Usability Scale

  1. Jeg tror godt, at jeg kunne tænke mig at bruge systemet ofte.
  2. Jeg synes, at systemet var unødigt kompliceret at bruge.
  3. Jeg synes, at systemet var nemt at bruge.
  4. Jeg tror, at jeg ville få brug for support fra en tekniker for at kunne bruge systemet.
  5. Jeg synes, at mange af systemets funktioner var godt integreret med hinanden.
  6. Jeg synes, at systemet var usammenhængende.
  7. Jeg tror, at de fleste hurtigt kan lære at bruge dette system.
  8. Jeg synes, at systemet var meget besværligt at bruge.
  9. Jeg følte mig sikker på, at jeg kunne bruge systemet.
  10. Jeg var nødt til at lære en masse ting, for at komme i gang med at bruge systemet.

Adaption by

Julie Christine S. Hvidt, Lone Fisker Christensen, Christian Sibbersen, Stig Helweg-Jørgensen, Jens Peter Hansen & Mia Beck Lichtenstein

The French System Usability Scale

  1. Je voudrais utiliser ce système fréquemment.
  2. Ce système est inutilement complexe.
  3. Ce système est facile à utiliser.
  4. J’aurais besoin du soutien d’un technicien pour être capable d’utiliser ce système.
  5. Les différentes fonctionnalités de ce système sont bien intégrées.
  6. Il y a trop d’incohérences dans ce système.
  7. La plupart des gens apprendront à utiliser ce système très rapidement.
  8. Ce système est très lourd à utiliser.
  9. Je me suis senti·e très en confiance en utilisant ce système.
  10. J’ai eu besoin d’apprendre beaucoup de choses avant de pouvoir utiliser ce système.

Adaptation by Guillaume Gronier & Alexandre Baudet

The German System Usability Scale

  1. Ich denke, dass ich das System gerne häufig benutzen würde.
  2. Ich fand das System unnötig komplex.
  3. Ich fand das System einfach zu benutzen.
  4. Ich glaube, ich würde die Hilfe einer technisch versierten Person benötigen, um das System benutzen zu können.
  5. Ich fand, die verschiedenen Funktionen in diesem System waren gut integriert.
  6. Ich denke, das System enthielt zu viele Inkonsistenzen.
  7. Ich kann mir vorstellen, dass die meisten Menschen den Umgang mit diesem System sehr schnell lernen.
  8. Ich fand das System sehr umständlich zu nutzen.
  9. Ich fühlte mich bei der Benutzung des Systems sehr sicher.
  10. Ich musste eine Menge lernen, bevor ich anfangen konnte das System zu verwenden.

Translation by Rummet et al. picked by Tobias J. Brix, Alice Janssen, Michael Storck, Julian Varghese

The Greek System Usability Scale

  1. Νομίζω οτι θα ήθελα να χρησιμοποιώ αυτό το σύστημα συχνά.
  2. Βρήκα αυτό το σύστημα αδικαιολόγητα περίπλοκο.
  3. Σκέφτηκα ότι αυτό το σύστημα ήταν έυκολο στη χρήση.
  4. Νομίζω οτι θα χρειαστώ βοήθεια από κάποιον τεχνικό για να είμαι σε θέση να χρησιμοποιήσω αυτό το σύστημα.
  5. Βρήκα τις διάφορες λειτουργίες σε αυτό το σύστημα καλά ολοκληρωμένες.
  6. Σκέφτηκα οτι υπήρχε μεγάλη ασυνέπεια σε αυτό το σύστημα.
  7. Φαντάζομαι οτι οι περισσότεροι άνθρωποι θα μάθουν να χρησιμοποιούν αυτό το σύστημα πολύ γρήγορα.
  8. Βρήκα αυτό το σύστημα πολύ περίπλοκο/δύσκολο στη χρήση.
  9. Ένιωσα πολύ σίγουρος/η χρησιμοποιώντας αυτό το σύστημα.
  10. Χρειάστηκε να μάθω πολλά πράγματα πριν μπορέσω να ξεκινήσω με αυτό το σύστημα.

Adaptation by Christos Katsanos, Nikolaos Tselios, Michalis Xenos

The Indonesian System Usability Scale

  1. Saya berpikir akan menggunakan sistem ini lagi.
  2. Saya merasa sistem ini rumit untuk digunakan.
  3. Saya merasa sistem ini mudah untuk digunakan.
  4. Saya membutuhkan bantuan dari orang lain atau teknisi dalam menggunakan sistem ini.
  5. Saya merasa fitur-fitur sistem ini berjalan dengan semestinya.
  6. Saya merasa ada banyak hal yang tidak konsisten (tidak serasi) pada sistem ini.
  7. Saya merasa orang lain akan memahami cara menggunakan sistem ini dengan cepat.
  8. Saya merasa sistem ini membingungkan.
  9. Saya merasa tidak ada hambatan dalam menggunakan sistem ini.
  10. Saya perlu membiasakan diri terlebih dahulu sebelum menggunakan sistem ini.

Adaptation by Zahra Sharfina, Harry Budi Santoso

The Malay (Mobile) System Usability Scale

  1. Saya rasa saya ingin kerap menggunakan aplikasi mudah alih ini.
  2. Saya rasa aplikasi mudah alih ini sesuatu yang rumit.
  3. Saya rasa aplikasi mudah alih ini mudah untuk digunakan.
  4. Saya memerlukan bantuan daripada orang lain untuk menggunakan aplikasi mudah alih ini.
  5. Saya mendapati fungsi-fungsi dalam aplikasi mudah alih ini saling bersepadu (berhubungkait) dengan baik.
  6. Saya rasa terdapat banyak kandungan di dalam aplikasi mudah alih ini yang tidak konsisten antara satu sama lain.
  7. Saya membayangkan bahawa kebanyakan orang akan cepat belajar menggunakan aplikasi mudah alih ini.
  8. Saya mendapati aplikasi mudah alih ini leceh untuk digunakan.
  9. Saya berasa yakin menggunakan aplikasi mudah alih ini.
  10. Saya perlu belajar terlalu banyak perkara sebelum boleh menggunakan aplikasi mudah alih ini.

Adaptation by Muhamad Fadhil Mohamad Marzuki, Nor Azwany Yaacob, Najib Majdi Yaacob

The Polish System Usability Scale

  1. Myślę, że często używałbym/używałabym tego systemu.
  2. Odbieram ten system jako niepotrzebnie skomplikowany.
  3. Myślę, że system jest łatwy w użyciu.
  4. Myślę, że potrzebowałbym/potrzebowałabym wsparcia asystenta, aby używać tego systemu.
  5. Uważam, że różne funkcje tego system są dobrze zintegrowane.
  6. Myślę, że w tym systemie jest za dużo niespójności.
  7. Wydaje mi się, że większość ludzi nauczyłaby się bardzo szybko używać tego systemu.
  8. Odbieram ten system jako bardzo niewygodny w użyciu.
  9. Czułem/czułam się bardzo pewnie używając tego systemu.
  10. Musiałem/musiałam nauczyć się wielu rzeczy, zanim zacząłem/zaczęłam właściwie posługiwać się tym systemem.

Adaptation by Anna Borkowska and Katarzyna Jach

The European Portuguese System Usability Scale

  1. Acho que gostaria de utilizar este produto com frequência.
  2. Considerei o produto mais complexo do que necessário.
  3. Achei o produto fácil de utilizar.
  4. Acho que necessitaria de ajuda de um técnico para conseguir utilizar este produto.
  5. Considerei que as várias funcionalidades deste produto estavam bem integradas.
  6. Achei que este produto tinha muitas inconsistências.
  7. Suponho que a maioria das pessoas aprenderia a utilizar rapidamente este produto.
  8. Considerei o produto muito complicado de utilizar.
  9. Senti-me muito confiante a utilizar este produto.
  10. Tive que aprender muito antes de conseguir lidar com este produto.

Adaptation by Ana Isabel Martins,*, Ana Filipa Rosa, Alexandra Queirós, Anabela Silva, Nelson Pacheco Rocha

The Spanish System Usability Scale

  1. Me gustaría usar esta herramienta frecuentemente.
  2. Considero que esta herramienta es innecesariamente compleja.
  3. Considero que la herramienta es fácil de usar.
  4. Considero necesario el apoyo de personal experto para poder utilizar esta herramienta.
  5. Considero que las funciones de la herramienta están bien integradas.
  6. Considero que la herramienta presenta muchas contradicciones.
  7. Imagino que la mayoría de las personas aprenderían a usar esta herramienta rápidamente.
  8. Considero que el uso de esta herramienta es tedioso.
  9. Me sentí muy confiado al usar la herramienta.
  10. Necesité saber bastantes cosas antes de poder empezar a usar esta herramienta.

Adaptation by Magdalena Del Rocio Sevilla-Gonzalez, Lizbeth Moreno Loaeza, Laura Sofia Lazaro-Carrera, Brigette Bourguet Ramirez, Anabel Vázquez Rodríguez, María Luisa Peralta-Pedrero, Paloma Almeda-Valdes

The Slovene System Usability Scale

  1. Menim, da bi ta sistem rad pogosto uporabljal.
  2. Sistem se mi je zdel po nepotrebnem zapleten.
  3. Sistem se mi je zdel enostaven za uporabo.
  4. Menim, da bi za uporabo tega sistema potreboval pomoč tehnika.
  5. Različne funkcije tega sistema so se mi zdele dobro povezane v smiselno celoto.
  6. Sistem se mi je zdel preveč nekonsistenten.
  7. Menim, da bi se večina uporabnikov zelo hitro naučila uporabljati ta sistem.
  8. Sistem se mi je zdel neroden za uporabo.
  9. Pri uporabi sistema sem bil zelo suveren.
  10. Preden sem osvojil uporabo tega sistema, sem se moral naučiti veliko stvari.

Adaptation by Bojan Blažica and James R. Lewis


[2] Brooke, J. (1996). SUS: A ‘quick and dirty’ usability scale. In P.W. Jordan, B. Thomas, B.A. Weerdmeester, & I.L. McClelland (Eds.) Usability Evaluation in Industry (pp. 189-194). Taylor & Francis: London.

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