Major Religions Ranked by Size: "The adherent counts presented in the list above are estimates of the number of people who have at least a minimal level of self-identification as adherents of the religion"

David B. Barrett's World Christian Encyclopedia(1994 update) gives an oft-cited figure of 1.9 billion Christians (or about 33% of the world population), and has projected that by the year 2000 there will be 2.1 billion Christians in the world. Regardless of the degree of accuracy of this figure, Christianity, if taken as a whole, is unarguably the largest world religion.

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Focus on Religion 2001 UK census

The 2001 Census identified 8.6 million people in Great Britain who said they had no religion. Christianity is the main religion, with 41 million people. Muslims were the largest non-Christian religious group – 1.6 million – and their profile shows a young, tightly clustered, but often disadvantaged, community.

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The Families of Christianity

Branch - - Numbers
Catholic - - 968,000,000
Protestant - - 395,867,000
Other - - 275,583,000
Orthodox - - 217,948,000
Anglicans - - 70,530,000

(source: Encyclopedia Britannica)

Breaking these families down by "denomination," begins to uncover even greater diversity.

Branch - - Numbers
Catholic - - 1,050,000,000
Orthodox/Eastern Christian - - 240,000,000
African indigenous sects - - 110,000,000
Pentecostal - - 105,000,000
Reformed/Presbyterian/Congregational - - 75,000,000
Anglican - - 73,000,000
Baptist - - 70,000,000
Methodist - - 70,000,000
Lutheran - - 64,000,000
Jehovah's Witnesses 1 - - 4,800,000
Adventist - - 12,000,000
Latter Day Saints - - 11,500,000
Apostolic/New Apostolic 1 - - 0,000,000
Stone-Campbell ("Restoration Movement") - - 5,400,000
New Thought (Unity, Christian Science, etc.) - - 1,500,000
Brethren (incl. Plymouth) - - 1,500,000
Mennonite - - 1,250,000
Friends (Quakers) - - 300,000