Neilson Norman Group is a leader in the User Experience (UX) field, and they believe that five users are enough to tell you if your design project is a hit or a miss. It is interesting to see where the magic number 5 came from and why they thought of this principle in usability testing.
This number still shocks stakeholders and designers, and they ask questions like, “Really? We don’t need long usability tests, and just five users would do?”. It’s relief providing thought we know, but hold on and read this blog post to know why numbers and logic back this rule.
Another principle that supports this rule is the Pareto principle or the 80/20 rule, which states that 80 per cent of the information comes from 20 per cent of the source. So, by noticing the behaviour of only five users, you’re not missing out on a lot of information.
The Origin of the “5-User” Rule
Jakob Nielsen has a Ph.D. and is a usability pioneer who co-founded the Nielsen Norman Group with Dr. Don Norman. His famous 5-user rule states that five users are enough to uncover 85% of usability problems in a product. After a few users, you see a repetitive pattern in the fewer insights you get, making the tests less effective and more resource-consuming.
There’s a law in economics, the Law of diminishing marginal utility, which states that satisfaction from consuming a product or service decreases with each additional unit consumed. The more of something you consume, the less effect it has on you with every additional unit you consume.
Consider this law in association with Jakob Nielson’s famous rule; it will make a lot of sense.
Reasoning Behind the 5-User Rule
Why five users? Why not less, and why not more?
Well, count on us to see what each user brings.
Starting with 0, it’s common sense that zero users will bring zero insights, so you need more.
1 user: Now, you have at least some data to analyse, but it’s not enough. Why go beyond one user if we are talking about minimalism? With one user, there’s always a possibility of being misled by the spurious behaviour of just one user, as it can misrepresent the sample size.
2nd user: Your insights shoot up, and now you don’t have to rely on one person to draw inferences. Now, you will notice that this user behaved slightly differently than the first user but also had some similarities. There will be some overlap of information to draw analysis from this information.
3rd user: This user will not do many new things; you would have already seen this behaviour in the first or second user. However, this user will validate the information gathered earlier while providing a small amount of new data.
Now, beyond this, you can add up to 5 users, but you are wasting time and resources beyond five. More and more users doesn’t mean more and more knowledge, but it means more and more confusion. You will continuously see the same thing, which leads to no conclusion.
More than attempting to add users for usability testing, keep your focus on designing the site with the insights the initial five users supplied.
How to Strategically Scale Usability Testing When Necessary
Listen to this theory if you’re still unconvinced and want to test the design on a larger scale. Run multiple rounds of 5 user tests. Let’s say you’re trying to perform usability testing on 15 users. We suggest distributing these 15 users in 3 batches and conducting usability tests thrice with those three batches.
The reasoning behind this logic is that it is better to distribute groups of users between different groups of usability testing so that you can test out different features of the same product.
You can spend the budget on three studies with five users each. After the first round of testing, you will find the design’s weaknesses, but there’s still room for improvement. You will find 85% of the usability problems in the design; now, you fix these problems and develop an iterative design.
In the redesigned website, now you will need to test again. Now, you can use the second batch of users to test this new design. It’s assumed that the redesign would have solved all the problems, but designs are rarely close to perfection and can always be improved.
After the second round of iteration based on the second batch of 5 users, you can now use the third batch for the 3rd redesigned website. This way, you further improve your design with every batch of users, as there’s always scope for improvement. With the new redesign, you might find problems that weren’t noticeable before, but now they are, and you can fix them.
Issues like information structure and task flows aren’t noticed and solved in the first round of the iteration process because, in the initial studies, users are focused on surface-level information. So, three studies with five users each will be a much better choice over a single huge study of 15 users.
Apply the 5-User Rule in 5 Steps
In 5 easy steps, learn to apply the five-user rule in your upcoming design project.
Step 1: State your Goals
Define what you wish to achieve in the design project. Is your focus on navigation, task flow, accessibility, UI, or something else? To achieve something, you need to know what you want to achieve.
Step 2: Pick Representative Users
Because you select only five users, ensure that all of them accurately represent the target audience you want to reach. For instance, products with multiple users test across groups. Apps like Unacademy, an educational platform, will test with three students and two teachers (or vice versa) to capture diverse user behaviour.
Step 3: Run Multiple Test
As mentioned above, run multiple small tests with five users each instead of a single large test. Iterative designs are the best ones.
Step 4: Blend Qualitative and Quantitative Data
Designers usually prioritise quantitative data, such as completion or error rates and overlook qualitative data, but that should not be the case.
Step 5: Research to Adapt
There are no hard and fast rules to anything; customise your approach based on the ongoing research outputs. Five users will be enough for exploratory studies, but adjust your sample size accordingly for the latter part of the research. Techniques like card sorting or tree testing are statistically important.
When You Need More Than 5 Users
There must be instances where five users will not do so, and you will need more users to test your product. In an app or website with several distinct groups of users, you will need a bigger sample size to represent the interests of different groups fairly.
For instance, there are apps where children and parents must use the platform, so this highly diverse audience needs different sets of representatives in the sample size. Apps like Ola and Uber allow customers and riders to log in to the app and expect different things from the usability standards.
Other platforms where purchasing agents get connected by sales staff also have significant differences between the observations from the two groups. These platforms need more than five users.
What is the Future of Usability Testing?
In conclusion, let us give you a sneak peek of how usability testing will pan out in 2025. It’s unsurprising that AI and automation have taken the landscape and will continue to do so.
The core principle will be to perform user testing that is core, small, and vital. Advanced tools, for sure, can analyse a ton of data and track user behaviour, but these technologies can’t replace the simplicity of the five-user test as it continues to shine.
Contact Yellow Slice’s team of UI/UX designers to make your next project a big hit. Our designers employ refreshing, unique ideas and age-old principles that stand the test of time in design.
Frequently Asked Questions (FAQs)
1. What are the pros of testing UX design with five users?
First and foremost, testing with only five users is economical; hence, it’s good practice for startups with low budgets. Because you are dealing with a small user group, you can detect specific and broad issues to focus on. In the new age of 2025, agile development asks for rapid feedback cycles, and if the user batches are small, then you can practice the usability testing again and again.
2. What are the cons of relying solely on five users for usability testing?
There have been many success stories of the 5-user rule, but it comes with risks. Employing only five users can result in misleading information because you don’t have enough information. Some products’ user diversity is higher due to global audiences or varied demographics and personas.
