According to the Guinness Book of World Records, Islam is the world's fastest-growing religion by number of conversions each year: "Although the religion began in Arabia, by 2002 80% of all believers in Islam lived outside the Arab world. In the period 1990-2000, approximately 12.5 million more people converted to Islam than to Christianity". Part of the book's quote can be seen online from this excerpt from Google Books. This was again shown in the 2005, 50th anniversary edition of Guinness Book of World Records, although the number of conversions was not mentioned this time.
In 1990, 935 million people were Muslims. According to the BBC, a comprehensive American study concluded in 2009 the number stood at approximately 23% of the world population with 60% of Muslims living in Asia. The report was done by the Pew Forum Research Centre. The forum also projected that in 2010 out of the total number of Muslims in the world 62.1% will live in Asia.
However the report also included a statement saying "While the global Muslim population is expected to grow at a faster rate than the non-Muslim population, the Muslim population nevertheless is expected to grow at a slower pace in the next two decades than it did in the previous two decades. From 1990 to 2010, the global Muslim population increased at an average annual rate of 2.2%, compared with the projected rate of 1.5% for the period from 2010 to 2030". The report also made reference to the fact that Muslims are estimated to make up 23.4% of the total global population in 2010 (out of a total of 6.9 billion people) and that by 2030 Muslims will represent about 26.4% of the global population (out of a total of 7.9 billion people). The Pew report also highlights that there is insufficient data available on religious conversion from its own findings given the complexities of identity and the difficulties of obtaining data: "Statistical data on conversion to and from Islam are scarce. What little information is available suggests that there is no substantial net gain or loss in the number of Muslims through conversion globally.
Islam is Fastest Growing Religion All Over The World