Islam, the second largest religion in the world, has over 1.6 billion followers worldwide – 23% of the world’s population. Indonesia, Pakistan, and India top the list with the largest Muslim populations – they each hold around 200 million, 175 million and 176 millions Muslims respectively. Morocco, Somalia, Afghanistan, Tunisia, Iran, and Western Sahara all near 100 percent Islamic populations.
http://www.pewforum.org/2015/04/02/muslims/pf_15-04-02_projectionstables74/