The global Muslim population stands at 1.57 billion, meaning that nearly one in four people in the world practice Islam, according to a report last week that was billed as the most comprehensive of its kind.
The Pew Forum on Religion and Public Life report provides a precise number for a population whose size has long has been subject to guesswork, with estimates ranging from 1 billion to 1.8 billion.
The project, three years in the making, also presents a portrait of the Muslim world that might surprise some people. For instance, Germany has more Muslims than Lebanon, China has more Muslims than Syria, Russia has more Muslims than Jordan and Libya combined, and Ethiopia has nearly as many Muslims as Afghanistan.
"This whole idea that Muslims are Arabs and Arabs are Muslims is really just obliterated by this report," said Amaney Jamal, an assistant professor of politics at Princeton University who reviewed an advance copy.
Pew officials call the report the most thorough on the size and distribution of adherents of the world's second-largest religion behind Christianity, which has an estimated 2.1 billion to 2.2 billion followers.
Christianity is still the dominant faith in the United States. According to Pew's 2008 U.S. Religious Landscape Survey, 79.5 percent of U.S. citizens claim some form of Christian faith, from mainline Protestant to Jehovah's Witnesses. Evangelical Protestants account for 26 percent of that group.
Only 1 percent of the United States population is Muslim, according to the 2008 survey, and in Kentucky, only 0.5 percent of the state's 4.3 million residents are Muslim.
The arduous task of determining the Muslim populations in 232 countries and territories involved analyzing census reports, demographic studies and general population surveys, the report says. In cases in which the data was a few years old, researchers projected 2009 numbers.
The report also sought to pinpoint the world's Sunni-Shiite breakdown, but difficulties arose because so few countries track sectarian affiliation, said Brian Grim, the project's senior researcher.
As a result, the Shiite numbers are not as precise; the report estimates that Shiites represent between 10 and 13 percent of the Muslim population, in line with or slightly lower than other studies. As much as 80 percent of the world's Shiite population lives in four countries: Iran, Pakistan, India and Iraq.
The report provides further evidence that although the heart of Islam might beat in the Middle East, its greatest numbers lie in Asia: More than 60 percent of the world's Muslims live in Asia.
About 20 percent live in the Middle East and North Africa, 15 percent live in Sub-Saharan Africa, 2.4 percent are in Europe and 0.3 percent are in the Americas. The Middle East and North Africa have fewer Muslims overall than Asia, but the region easily claims the most Muslim-majority countries.
Those population trends are well established, but the large numbers of Muslims who live as minorities in countries aren't scrutinized as closely. The report identified about 317 million Muslims — one-fifth of the world's Muslim population — living in countries where Islam is not the majority religion.
About three-quarters of Muslims living as minorities are concentrated in five countries: India (161 million), Ethiopia (28 million), China (22 million), Russia (16 million) and Tanzania (13 million).
In several of these countries — including India, Nigeria, China and France — divisions featuring a volatile mix of religion, class and politics have contributed to tension and bloodshed among groups.
