Do you mean the number of descendants from whom you are just descended? You could probably just count. Or the total number of descendants- if that's the case, chances are there are hundreds of them. You'd have to go through each of the individuals who are descendants and see if they had siblings and children, and do it for each of those individuals as well. Eventually you'll probably hit a few brick walls or run into private profiles. It might be a bit easier if you took an autosomal DNA test with Ancestry so you can see if there are any related surnames in your matches' trees.