Check out this AP article: "Report: Global Muslim population hits 1.57 billion"
So, going off the U.S. Census Bureau's population estimation of 6,789,349,164, that means 23% of the world is Muslim.
Other tidbits?
Two-thirds of all Muslims live in 10 countries (Indonesia, Pakistan, India, Bangladesh, Iran, Turkey, Egypt, Algeria, Morocco and Nigeria).
Muslims are 0.8 percent of the population in the US, and 2 percent in Canada.