Out of the 6 billion or so people in the world right now, how many would consider themselves religious?

Any Introduction to Sociology Textbook would have the numbers on world
religions, and www.adherents.com provides wonderful info on world
religions.  Their 2005 snapshot shows that 33% of the worlds
inhabitants, some 2.2 billion people, consider themselves Christian
(some 1.2 billion of those Christians are Catholic).  About 21% are
follower of Islam (1.5 billion).  Hindus make up 14%.  The really new
category this past century are the growing numbers who consider
themselves “non-religious,” some 16% of the planet.

For Catholics in the USA, the numbers are challenging.  “The Catholic
Church has lost more adherents than any other group: about one-third of
respondents raised Catholic said they no longer identified as such.
Based on the data [35,000 persons in a Pew Forum Study, U.S. Religious
Landscape], the survey showed, ‘this means that roughly 10 percent of
all Americans are former Catholics’ ” (New York Times, Feb 25, 2008).
Some 30 million Americans are “former Catholics,” the second largest
religious group in the country.  The Catholic Church and the U.S. Census
report some 70 million Americans, roughly 23% of the population, are

Overall in the USA, huge changes are occurring as people switch and swap
faiths through their lifetimes, and many consider themselves “spiritual
but not religious.”  The American Religious Identification Survey
conducted By Komin and Keysar out of Trinity College in March 2008
) reports fascinating findings.  “86% of American adults identified as
Christians in 1990 and 76% in 2008.  The challenge to Christianity in
the U.S. does not come from other religions but rather from a rejection
of all forms of organized religion.  34% of American adults considered
themselves “Born Again or Evangelical Christians” in 2008.  The U.S.
population continues to show signs of becoming less religious, with one
out of every five Americans failing to indicate a religious identity in
2008. The “Nones” (no stated religious preference, atheist, or agnostic)
continue to grow, though at a much slower pace than in the 1990s, from
8.2% in 1990, to 14.1% in 2001, to 15.0% in 2008.  Asian Americans are
substantially more likely to indicate no religious identity than other
racial or ethnic groups.   One sign of the lack of attachment of
Americans to religion is that 27% do not expect a religious funeral at
their death.  America’s religious geography has been transformed since
1990. Religious switching along with Hispanic immigration has
significantly changed the religious profile of some states and regions.
Between 1990 and 2008, the Catholic population proportion of the New
England states fell from 50% to 36% and in New York it fell from 44% to
37%, while it rose in California from 29% to 37% and in Texas from 23%
to 32%” (Komin and Keysar, 2008, Summary, p.1)