...... but, just for you, we'll assume:
...... an mp3 is 4MB - so that's 250 per GB, giving a total of 8000 for a 32GB drive.
...... a picture is 1MB, giving a total of 32000 for a 32GB hard drive.
...... movies are 2GB, giving a total of 16 for a 32GB hard drive.
These figures are very approximate as, like Chuck said, there are lots of variables.