Usability Calculator

Project background

As a UX designer, one of the most essential tools for evaluating usability is the System Usability Scale (SUS). SUS provides a quick and reliable way to measure usability through a standardised 10-question survey, making it a staple in user research and industry benchmarking. Over time, I found myself calculating SUS scores regularly in my own work to assess the effectiveness of design solutions and make informed improvements.

Goal

This project began as a personal need to streamline the SUS calculation process and evolved into a helpful resource for others in the UX community. My goal was to build a straightforward, reusable calculator that automates the SUS score calculation, allowing both UX designers and researchers to quickly interpret usability data. The process involved concept planning, implementing the calculator in JavaScript, and thorough testing and iteration to ensure accurate results.

Feature highlights

The calculator is:

• Mobile friendly and fully responsive
• Adhering to accessibility guidelines such as minimum touch targets and sufficient colour contrast.
• Quick and intuitive to use with instant results

Building the calculator

Planning

The concept was straightforward: create a 10-question form with clickable buttons for each answer, making the SUS survey easy to complete. By keeping the layout simple and clean, users can interact with the tool quickly and intuitively.

Tooling decision

JavaScript was chosen for its simplicity and speed. It allows the calculator to work directly on websites, providing instant feedback without the need for additional software or a backend.

Challenges

SUS calculations are more complex than simple percentages, with each response being adjusted by specific weightings:

• Odd-numbered Questions: Subtract 1 from each answer.
• Even-numbered Questions: Subtract each answer from 5.

The adjusted scores are then summed (out of 40) and multiplied by 2.5 to get a final score on a 0–100 scale. This unique calculation ensures consistency with industry benchmarks, allowing for reliable comparison with other products.

Enhancing usability

To make the results more actionable, I added an interpretation guide that explains the meaning of different score ranges. Users can quickly see where their product stands and how it compares to industry standards, helping them identify usability strengths and areas for improvement.

The calculator

Go ahead and try out the calculator below! It's easy to use and provides instant results.

How to use the calculator

1. Create and distribute the survey to participants using Microsoft Forms, Google Forms or even printed on paper.
2. Enter the user responses to each of the 10 SUS questions in the calculator below.
3. After all responses are entered, select Calculate to see the SUS score and interpretation.

Interpreting the results

SUS (System Usability Scale) is a widely-used tool to evaluate the usability of products, interfaces, and digital solutions. SUS scores provide a benchmark across many products, allowing designers to see how their solution stacks up against others. This comparison helps designers assess whether their product is meeting, exceeding, or falling short of industry standards. The SUS score is based on a 0–100 scale, where scores above 68 indicate above-average usability and scores below 68 suggest room for improvement.

Score ranges and what they mean

• 85–100: Excellent Usability – Generally, this is the top range of usability and indicates a highly effective, user-friendly design.
• 68–84: Good Usability – A solid score indicating that most users found the experience smooth and intuitive.
• 50–67: Average Usability – Usable, but with areas for improvement.
• Below 50: Poor Usability – Indicates issues in user experience and usability that may be causing friction.

Empowering usability assessment

Creating this SUS calculator has been an enriching experience, merging my skills in UX and web development to develop a tool that supports designers in evaluating usability. By automating the calculation process, I hope this tool makes it easier for others to quickly assess and benchmark their products, helping them gain insights and identify areas for improvement. As usability remains a top priority in product design, this calculator serves as a small but valuable resource in ensuring designs deliver the best possible user experience.

Design credits

I created the calculator and its style, but elements of the top illustration were obtained from Pablita by Icons8.