Major Religions of the World
Islam: 1.5 billion
Christianity:
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
Source: http://www.quranhadith.org/new/Major%20Religions%20of%20the%20World.htm
The Classical World Religions List
There are twelve classical world religions. This is the list of religions described most often in surveys of the subject, and studied in World Religion classes (some of them more for historical rather than contemporary reasons):
Islam
Baha'i
Buddhism
Christianity
Confucianism
Hinduism
Jainism
Judaism
Shinto
Sikhism
Taoism
Zoroastrianism
The "World's Major Religions" list published in the New York Public Library Student's Desk Reference is typical of world religion lists which are functionally-oriented, yet still strongly classical (New York: Prentice Hall, 1993; pg. 271):
Islam
Baha'i
Buddhism
Confucianism
Hinduism
Judaism
Orthodox Eastern Church
Protestantism
Catholicism
Shinto
Taoism
Source: http://www.quranhadith.org/new/Major%20Religions%20of%20the%20World.htm