You will not find a "straight forward answer" until you can define what you mean by "size". A text file takes up a certain amount of disk space. The same content in a database as a simple blob field takes up a different amount. The same content in a Confluence system, and hence stored in a database takes up a different amount. Most databases will store differently, so both the database examples will vary by the type of database you are using. And most do some form of compression, so you'll need to take account of that too.
You could possibly try this solution, but you have to query the db. You could also search the marketplace for an app.