1. What is the range of "hundreds of thousands"? [100,000 - 999,999] and "tens of thousands" [10,000-99,000]? 2. I should say "hundreds of " if it is between "200 and 999", correct? Yes but sometimes people can use 'hundreds' in an exaggerated way to just mean a lot of something. It is also possible to say that one hundred (100) is captured by hundreds as well, even if it is a bit misleading. People might say this to create the impression that there are perhaps 500 when there are only 100. Strictly speaking 100 is in the hundreds, even if there is only one of them. 3.What if I want to say something between "20 and 99", what should I say? You can say tens or dozens (lots of 12) If there are more similar expressions like this, please let me know. Thank you in advance. For adolescent people you can talk about the 'teens' of 13-19 - thirteen, fourteen.... http://www.englishlessonsbrighton.co.uk/saying-large-numbers-english/