A think tank called Foreign Policy (www.foreignpolicy.com) developed a list of the fastest growing religions. It found that out of the earth’s population (over 6 billion) that Christianity has nearly 2.2 billion believers. Islam has 1.3 billion followers and Hinduism 870 million.

Another website (http://www.adherents.com/Religions_By_Adherents.html) gave similiar numbers of 2.1 billion Christians and 1.5 billion Muslims.

Those numbers could be deceiving since many say they are followers because of habit, tradition and cultural influences and not because of a true heart transformation.  It's probably less.