Probably the easiest way to answer that would be to mount the file system on your computer, and check the contents of all those folders (even just right-click, properties, and look at the folder size.)
For me, I'm using about 5 GB. 0.5 in Music, 4.1 in Videos, and a little here and there in other stuff. My DCIM (camera photos) takes up roughly 0.2 GB, but I keep it trim.