System Usability Scale (SUS)

By Dnyaneshwar N • 5 min read • John Brooke, 1986

The industry gold standard for quantitative usability benchmarking. A SUS score above 68 is considered average; scores above 80 indicate world-class user experience.

Core Principle

A standardized 10-item Likert scale questionnaire yielding a single composite score from 0 to 100 to quantify perceived product usability.

The Industry Benchmark for Quantitative Usability

Created by John Brooke in 1986, the System Usability Scale (SUS) is a 10-item questionnaire that provides a quick, reliable, and standardized metric of perceived system usability.

Users respond to ten alternating positive and negative statements on a 5-point Likert scale (from Strongly Disagree to Strongly Agree). Scores are converted into a composite score from 0 to 100.

A SUS score of 68 represents the global average across thousands of evaluated software applications. Products scoring above 80 are considered world-class; products below 50 indicate severe usability and adoption risks.

Benchmarking Usability Before and After AI Integration

When products introduce complex AI features, teams often assume usability will automatically improve because tasks are automated. In reality, unexpected AI behaviors and complex prompting flows can actually degrade perceived usability.

The System Usability Scale is an invaluable diagnostic benchmark during AI migrations. By administering the SUS before and after integrating automated tools, teams can empirically verify whether the automation simplified the experience or introduced cognitive confusion.

If the SUS score drops, the team can immediately evaluate trust calibration, error recovery, and system predictability to restore effortless interaction.

Frequently Asked Questions

Administering and interpreting the System Usability Scale:

What is a good SUS score? A score of 68 is average (Grade C); 80 or higher is excellent (Grade A); 90 or higher is world-class.
Is the SUS score a percentage? No. A SUS score is a percentile ranking reflecting overall perceived usability, not a percentage of correct tasks.
How many participants are needed for a reliable SUS score? A sample size of 8 to 12 participants is generally sufficient to detect major usability trends and benchmark iterations.

When to Apply

Post-usability test surveys and quarterly product UX benchmarking
Measuring redesign impact against legacy software baselines
Cross-product enterprise software usability audits
Presenting objective UX ROI metrics to executive leadership
Standardize usability benchmarks across sprint cycles using How to Test UX Design Decisions Before Development.

Recommended Practices

Administer the 10-question survey immediately following a completed usability test.
Calculate composite scores using the standard alternating odd/even scoring formula.
Track SUS score progression over time across product releases.
Combine quantitative SUS scoring with qualitative inspection from Nielsen's 10 Usability Heuristics.

Practices to Avoid

Do not modify the phrasing of the 10 standardized questions, which breaks benchmark validity.
Do not interpret SUS as a percentage (a score of 70 is not a grade of 70%, but above average).
Do not rely on SUS alone without pairing it with qualitative observations.

Diagnostic Checklist

Are usability evaluations paired with standardized SUS surveys?
Is the benchmark baseline recorded prior to releasing major UX redesigns?
Are low SUS question scores investigated with qualitative task video analysis?
Benchmark enterprise usability across desktop and mobile workflows in our Interactive UX Solutions & Prototypes.