Worldwide, more than eight-in-ten people identify with a religious group. A comprehensive demographic study of more than 230 countries and territories conducted by the Pew Research Center’s Forum on Religion & Public Life  estimates that there are 5.8 billion religiously affiliated adults and children around the globe, representing 84% of the 2010 world population of 6.9 billion. These five charts sum up the age, size, geography, and power of the world's major religions.
The study by the Pew Forum also finds that roughly one-in-six people around the globe (1.1 billion, or 16%) have no religious affiliation. This makes the unaffiliated the third-largest religious group worldwide, behind Christians and Muslims, and about equal in size to the world’s Catholic population.
The geographic distribution of religious groups varies considerably. A plurality of Jews (44%) live in North America, while about four-in-ten (41%) live in the Middle East and North Africa – almost all of them in Israel.
Nearly three-quarters (73%) of the world’s people live in countries in which their religious group makes up a majority of the population. Most members of the other major religious groups live in countries in which they are in the minority. Seven-in-ten Buddhists (72%), for example, live as religious minorities.
Muslims are a majority in 49 countries, including 19 of the 20 countries in the Middle East and North Africa. The religiously unaffiliated make up a majority of the population in six countries, of which China is by far the largest. (The others are the Czech Republic, Estonia, Hong Kong, Japan and North Korea.)
Some religions have much younger populations, on average, than others. In part, the age differences reflect the geographic distribution of religious groups. Those with a large share of adherents in fast-growing, developing countries tend to have younger populations. Those concentrated in China and in advanced industrial countries, where population growth is slower, tend to be older. The median age of two major groups – Muslims (23 years) and Hindus (26) – is younger than the median age of the world’s overall population (28)
Source: Pew Forum