It found that Christians make up about 32% of the world's population, followed by Muslims, the second largest group, with 1.6 billion adherents.
Hindus were the third largest group, numbering about one billion (15%), followed by Buddhists, at 500 million (7%) and Jews, who number 14 million (0.2%.)
The worldwide demographic study of more than 230 countries and territories found that more than eight people in 10 -- about 5.8 billion people -- identify with a religious group.
More than 400 million people (6%) practice various folk traditions, including African traditional, aboriginal or folk religions, the global survey found.
The Pew Forum said that the study, in which religious affiliation was based on self-identification, did not attempt to measure the degree to which practitioners observe their faiths.