Why you only need to test with five users (explained)
One question I get a lot is, Do you really only need to test with 5 users? There are a lot of strong opinions about the magic number 5 in usability testing and much has been written about it. As you can imagine there isn’t a fixed number of users that will always be the right number (us quantitative folks love to say that) but testing with five users may be all you need for discovering problems in an interface, given some conditions.
The five user number comes from the number of users you would need to detect approximately 85% of the problems in an interface, given that the probability a user would encounter a problem is about 31%. Most people either leave off the last part or are not sure what it means.
