For an online tool, 5 is the maximum number of choices you should put in a list. Here’s why:
In 1956, a famous study by cognitive psychologist George A. Miller proposed the Magical Number Seven, Plus or Minus Two as the number of items people could remember. The study basically says that a person can store 5-9 items in their short term memory. So to be safe, a list of 5 items is the best choice.
Of course this concept has been over-applied in web design and there are several critical articles on this topic. There are clearly times when long lists make sense to browse through ordered information. However, when making decisions, too many options are proven to be overwhelming, especially when the answers need to be compared.
Most importantly, long lists have become even more troublesome on the small screens of smart phones. You should assume today that nearly half your users will be interacting with your software on mobile devices. So, if they can’t see the whole list at once, they will need to rely on their short term memory to recall the options. We’re back to 5!