Christianity > Anglican | Catholic | Evangelical | Jehovah's Witnesses | Latter-day Saints | Orthodox | Pentecostal Islam | Hinduism | Buddhism | Sikhism | Judaism | Baha'i | Zoroastrianism | more links (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: 1.5 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.

A major source for these estimates is the detailed country-by-country analysis done by David B. Barrett's religious statistics organization, whose data are published in the Encyclopedia Britannica (including annual updates and yearbooks) and also in the World Christian Encyclopedia (the latest edition of which - published in 2001 - has been consulted). Hundreds of additional sources providing more thorough and detailed research about individual religious groups have also been consulted.

This listing is not a comprehensive list of all religions, only the "major" ones (as defined below). There are distinct religions other than the ones listed above. But this list accounts for the religions of over 98% of the world's population. Below are listed some religions which are not in this listing (Mandeans, PL Kyodan, Ch'ondogyo, Vodoun, New Age, Seicho-No-Ie, Falun Dafa/Falun Gong, Taoism, Roma), along with explanations for why they do not qualify as "major world religions" on this list.

This world religions listing is derived from the statistics data in the Adherents.com database. The list was created by the same people who collected and organized this database, in consultation with university professors of comparative religions and scholars from different religions. We invite additional input. The Adherents.com collection of religious adherent statistics now has over 43,000 adherent statistic citations, for over 4,300 different faith groups, covering all countries of the world. This is not an absolutely exhaustive compilation of all such data, but it is by far the largest compilation available on the Internet. Various academic researchers and religious representatives regularly share documented adherent statistics with Adherents.com so that their information can be available in a centralized database.

Statistics and geography citations for religions not on this list, as well as subgroups within these religions (such as Catholics, Protestants, Karaites, Wiccans, Shiites, etc.) can be found in the main Adherents.com database.

This document is divided into the following sections:

After many centuries, with the increased Western awareness of Eastern history and philosophy, and the development of Islam, other religions were added to the list. Many Far Eastern ways of thought, in fact, were given the status of "world religion" while equally advanced religious cultures in technologically less developed or pre-literate societies (such as in Australia, Africa, South America, and Polynesia) were grouped together as pagans or "animists," regardless of their actual theology. It's true that by the standards applied at the time, the Far Eastern religions Westerners encountered were often in a different category altogether than the religions they classified as pagan. One can not directly compare, for example, the local beliefs of the Polynesian islands of Kiribati during the 1500s to the organizational, political, literary and philosophical sophistication of Chinese Taoism during the same period. But one could certainly question whether Japanese Shintoism, as an official "world religion", was theologically or spiritually more "advanced" than African Yoruba religion, which was classified simply as animism or paganism.

During the 1800s comparative religion scholars increasingly recognized Judaism, Christianity, Islam, Hinduism, and Buddhism as the most significant "world religions." Even today, these are considered the "Big Five" and are the religions most likely to be covered in world religion books.

Five smaller or more localized religions/philosophies brought the list of world religions to ten: Confucianism, Taoism, Jainism, Shinto and Zoroastrianism.

Beginning around 1900 comparative religion writers in England began to take note of the Sikhs which had begun to immigrate there from India (part of the British Empire at the time). Sikhs, if mentioned at all, had been classified as a sect of Hinduism during the first three hundred years of their history. But after the influential British writers began to classify Sikhism as a distinct, major world religion, the rest of the world soon followed their example.

The rest is here:
Major Religions Ranked by Size - Adherents.com