Major Religions of the World Ranked by Number of Adherents 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 thousandThis listing is not a comprehensive list of all religions, only the "major" ones . 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.How are adherents counted?There are five main methods for determining the number of adherents in a faith group:1. Organizational reporting: Religious bodies (such as churches or denominations) are asked how many adherents or members they have. This is the simplest and least expensive method, but it can be highly unreliable. Different faith groups measure membership differently. Some count as members only those who are actively attending services or who have passed through a lengthy initiation process. Others groups count all who have been baptized as infants and are thus on the church records, even though some of those people may have joined other faith groups as adults. Some groups over-report membership and others under-report membership. When asked what religion they consider themselves to be a part of, many may name a religion that does not have them on their rolls. In the United States, for instance, three times as many people claim to be Unitarian Universalists than are actually on church records.2. Census records: Many countries periodically conduct a comprehensive household-by-household census. Religious preference is often a question included in these census counts. This is a highly reliable method for determining the religious self-identification of a given population. But censuses are usually conducted infrequently. The latest census may be too old to indicate recent trends in religious membership. Also, many countries either have no accurate census data, or do not include questions regarding religious affiliation. It has been over fifty years since the United States included such a question in its national census, but Canada, India, New Zealand, Australia and other countries have very thorough, recent census data on the topic.3. Polls and Surveys: Statistical sampling using surveys and polls are used to determine affiliation based on religious self-identification. The accuracy of these surveys depends largely on the quality of the study and especially the size of the sample population. Rarely are statistical surveys of religious affiliation done with large enough sample sizes to accurately count the adherents of small minority religious groups.4. Estimates based on indirect data: Many adherent counts are only obtained by estimates based on indirect data rather than direct questioning or directly from membership roles. Wiccan groups have traditionally been secretive and often their numbers can only be estimated based on magazine circulations, attendance at conferences, etc. The counts of many ethnic-based faith groups such as tribal religions are