System Usability Scale (SUS) Calculator
Calculate standard 10-item System Usability Scale (SUS) scores (0-100), Sauro-Lewis letter grades (A+ to F), adjective ratings, percentile ranks, and export APA Chapter 4 usability tables.
How to Calculate SUS Scores in 3 Steps
Select your mode: 'Single Respondent' for immediate live evaluation or 'Multi-Respondent Matrix' for capstone cohorts.
Enter or paste responses for the 10 standard SUS items on a 1 (Strongly Disagree) to 5 (Strongly Agree) scale.
Instantly view the converted SUS score (0–100), Sauro-Lewis letter grade (A+ to F), adjective rating, and copy the Chapter 4 summary table.
System Usability Scale Evaluation Matrix
Industry-standard 10-item usability auditing engine for IT, Computer Science, and HCI capstone projects.
📝 Standard 10-Item Usability Survey (Brooke, 1986)
Scale: 1 = Strongly Disagree (SD), 2 = Disagree, 3 = Neutral, 4 = Agree, 5 = Strongly Agree (SA).
👥 Multi-Participant Data Matrix
Enter individual user response rows (each row contains 10 scores from 1 to 5).
| # | Participant | SUS Score | Del | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cohort Overall Mean SUS Score: | |||||||||||||
📋 APA 7th Chapter 4 System Usability Results Statement
Ready to copy directly into your thesis/capstone Chapter 4 evaluation narrative.
How to Calculate and Interpret System Usability Scale (SUS) Scores
In software engineering, Human-Computer Interaction (HCI), and Information Technology capstone research, validating that a newly developed system meets user expectations is essential for thesis defense approval. While ISO/IEC 25010 models measure technical software characteristics, the System Usability Scale (SUS)—developed by John Brooke in 1986—serves as the globally accepted gold standard for evaluating subjective perceived usability. Its 10-item instrument possesses remarkable psychometric reliability, producing high validity even with modest evaluation samples of 10 to 30 participants.
1. The Alternating Structure of the 10 SUS Items
The strength of SUS lies in its alternating positive and negative item design, which mitigates response acquiescence bias (the tendency for users to agree with all statements blindly):
- Odd Items (1, 3, 5, 7, 9 – Positive): e.g., "I thought the system was easy to use."
- Even Items (2, 4, 6, 8, 10 – Negative): e.g., "I found the system unnecessarily complex."
2. The Exact SUS Conversion and Scoring Algorithm
Novice researchers frequently assume that SUS scores represent simple percentages. In reality, raw responses on the 1-to-5 Likert scale undergo a two-step normal transformation:
- Convert Odd Item Scores: Subtract 1 from the raw score:
Contribution = X − 1(maps scores 1–5 to 0–4). - Convert Even Item Scores: Subtract the raw score from 5:
Contribution = 5 − X(maps scores 1–5 to 4–0, reversing the polarity). - Multiply Sum of Contributions by 2.5: Sum all 10 converted contributions (ranging from 0 to 40) and multiply by 2.5:
SUS Score = [ ∑ (X_odd - 1) + ∑ (5 - X_even) ] × 2.5This maps the total score onto a standardized 0 to 100 composite index.
3. Benchmark Interpretations: Sauro-Lewis & Bangor Models
Interpreting what a specific SUS score means requires benchmarking against global software usability databases:
- The 68.0 Average Threshold: A SUS score of exactly 68.0 represents the 50th percentile (Grade C). Systems scoring above 68.0 are above average.
- Grade A+ / A (80.3 to 100): Excellent usability. Represents the top 10% of software products. Users are strong promoters who recommend the tool organically.
- Grade B (74.1 to 80.2): Good usability. Highly acceptable with minor interface friction.
- Grade C (65.0 to 74.0): Marginal / OK. Baseline usability, but noticeable user friction exists.
- Grade D / F (Below 65.0): Not acceptable. High cognitive load, severe interface confusion, and high likelihood of user abandonment.
4. Reporting SUS in Thesis Chapter 4
When presenting SUS results in Chapter 4, report the overall mean score, standard deviation, sample size N, corresponding letter grade, and Bangor adjective rating:
"Usability testing of the developed portal yielded an overall mean SUS score of M = 82.50 (SD = 6.40, N = 20), corresponding to an 'A' letter grade and an 'Excellent' adjective rating under Sauro & Lewis (2012) benchmarks."
Frequently Asked Questions
What is the System Usability Scale (SUS)?
The System Usability Scale (SUS), created by John Brooke in 1986, is the global industry-standard "quick and dirty" reliable metric for measuring the perceived usability of software applications, mobile apps, and websites. It consists of 10 alternating positive and negative statements evaluated on a 5-point Likert scale (1 = Strongly Disagree, 5 = Strongly Agree).
What is the standard formula to compute a SUS score?
For each respondent: (1) For odd-numbered items (1, 3, 5, 7, 9), subtract 1 from the user's response: Score - 1. (2) For even-numbered items (2, 4, 6, 8, 10), subtract the user's response from 5: 5 - Score. (3) Sum all converted item scores (which ranges from 0 to 40) and multiply the sum by 2.5 to yield a final composite SUS score ranging from 0 to 100.
What is considered a "good" or passing SUS score in academic research?
Based on extensive empirical benchmarks by Sauro & Lewis (2012) across over 500 usability studies, the average industry SUS score is 68.0. A score of 68.0 corresponds to a grade of "C" and represents baseline acceptable usability. A score of 70 or above is considered "Good" (Acceptable), while scores of 80 or above represent "A-grade" Excellent usability.
Is a SUS score of 80 equal to 80% accuracy?
No. A SUS score is a composite index on a 0–100 scale, not a raw percentage. According to percentile distribution tables, a SUS score of 80.3 actually places the software in the top 10% (approximately the 90th percentile) of all evaluated software systems in existence.
How many respondents are needed for a SUS evaluation in an IT/CS capstone thesis?
According to Nielsen Norman Group research, testing with 5 to 10 representative end-users identifies over 80% of critical usability defects. For quantitative capstone evaluations in Philippine colleges, panels typically look for sample sizes between 15 and 30 participants (e.g., IT experts and target community end-users).