Apart from Christianity and Islam (which, respectively, rank 1st at 2.1 billion, and 2nd at 1.5 billion adherants), these are the world’s major religions ranked by number of adherants (according to this site):
- 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
- Jainism: 4.2 million
- Shinto: 4 million
- Cao Dai: 4 million
- Zoroastrianism: 2.6 million
- Tenrikyo: 2 million
- Neo-Paganism: 1 million
- Unitarian-Universalism: 800 thousand
- Rastafarianism: 600 thousand
- Scientology: 500 thousand