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

1 Christianity: 2.1 billion
2 Islam: 1.5 billion
3 Secular/Nonreligious/Agnostic/Atheist: 1.1 billion
4 Hinduism: 900 million
5 Chinese traditional religion: 394 million
6 Buddhism: 376 million
7 primal-indigenous: 300 million
8 African Traditional & Diasporic: 100 [...]