[Dr Philip Hardo]

Christianity: 2.1 billion
Islam: 1.3 billion
Secular/Nonreligious/Agnostic/Atheist: 1.1 billion
Hinduism: 900 million
Chinese traditional religion: 394 million
Buddhism: 376 million
primal-indigenous: 300 million

African Traditional & Diasporic: 100 million
Sikhism: 23 million
Juche: 19 million

Spiritism: 15 million
Judaism: 14 million
Baha'i: 7 million