How many subtopics is one allowed when writing an outline?

If the outline for English is for a paragraph/paper, there can be as many subtopics as you need to explain. Most teachers, even when they encourage their students to write a lot, do not want to read a lot. So, if you can combine similar sub-topics, try to. But as a person who writes long essays anyways, as far as I am concerned, you can have as many subtopics as you like. Just make sure your sub-topics refer back to whatever it is you are discussing. If you feel it is too long, or that the idea is similar, but it could stand on its own, make a new paragraph/topic.