Go through your top 10 artists and add up the total number of listeners. Divide that number by 10; this is the average number of listeners for your top ten. Now divide the average by the number of Radiohead fans (Radiohead is the artist with the most listeners). Multiply the result by 100–that is your "mainstream percentage".
1. James Newton Howard - 11,785 total listeners
2. Rob Zombie - 105,558 total listeners
3. Amethystium - 5,137 total listeners
4. System of a Down - 323,922 total listeners
5. Lacuna Coil - 88,635 total listeners
6. 崎元仁 - 3,920 total listeners…