http://www.adherents.com/Religions_By_Adherents.html
Major Religions of the World
Ranked by Number of Adherents
(Sizes shown are approximate estimates, and are here mainly for the purpose of ordering the groups, not providing a definitive number. This list is sociological/statistical in perspective.) - 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
- 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
Introduction
The adherent counts presented in the list above are current estimates of the number of people who have at least a minimal level of self-identification as adherents of the religion. Levels of participation vary within all groups. These numbers
tend toward the high end of reasonable worldwide estimates. Valid arguments can be made for different figures, but if the same criteria are used for all groups, the relative order should be the same. Further details and sources are available below and in the
Adherents.com main database.