In the Find admin UI, the Index Overview screens displays the total number of indexed objects, and the number of objects of each type. For more information, see http://webhelp.episerver.com/latest/find/explore-index.htm.

Thanks Bob, however I am only seeing "document type" and the number of objects. What I'm trying to find is the number of words inside each document type.

Are you interested in finding the total number of words in one specific property of an indexed item, or do you really want the count of all words in a completely indexed item? I ask because there is a lot of data that's being indexed for each item (by default), that a total word count for the entire item likely doesn't make a lot of sense. 

Maybe you can provide a sample use case or scenario for your situation? It might be better to understand what this term count is going to be used for.

@Chris, my use was to get an estimated word count of all indexed items (or for specific object types) in order to estimate translation costs of a website. I'm aware of the fact that the word count would be only an estimate, but even that would help.

For my current needs, I've now solved this with the help of Screaming Frog and its word count functionality. Even that is only a gross estimate, but it's at least something to start with.