Losing Our Religion: The third most common religious affiliation is non-religious.
A new study by the Pew Forum on Religion & Public Life ranked the world religions by numbers affiliated.
Christians are most populous with 2.2 billion adherents (32 percent of the world population), followed by Muslims with 1.6 billion devoted (23 percent).
Overall, the study found that more than eight in 10 (84 percent) of the world's 7 billion people adheres to some form of religion. But 16 percent of the world population report that they have no religious affiliation or they do not believe in God.
Their numbers come in at 1.1 billion worldwide. That's roughly the same number as the people who say they are Catholic.
"One out of six people does not have a religious identity," Conrad Hackett, a primary researcher and demographer on the study told the Washington Post. "But it is also striking that that overwhelming majority of the world does have some type of religious identity. So I think people will be surprised by either way of looking at it."