How many people were Islamic in 1000 AD?

Answer 1

It's really hard to find accurate demographic information from so long ago, as even today not all places keep records of religious affiliation.

However, at the peak of Rashidun Caliphate in 654 AD, about 40 million people or 19 percent of the world's population lived under Muslim rule. Most of these people became Muslim, as they were either Arabs who had come with the invading Arab armies or the progeny of these invaders, or they were forced to convert to Islam, or religious persecution under Islamic rule convinced them to convert to Islam. So we can say that less than 19% of the world in 654 AD was Muslim.

Under the Ummayad Caliphate from 661-750 this increased, through further Muslim conquests, to 62 million people or nearly 29% of the world's population.

Under the Abbasid Caliphate, which began in 750 and continued until 1517 when it fell to the Ottomans, the Muslims experienced a golden age and there was increased Arabization throughout the Caliphate. We can conclude an even larger percentage of people became Muslim throughout the empire at this time. At its demographic zenith in 850 AD, 50 million people lived in the Abbasid Caliphate or roughly 20% of the world's population. The majority were Muslim.

So... we can estimate that somewhere in the neighborhood of 50 million Muslims were living around 1000 AD, and they made up about 20% of the world's population. Which is the same percentage they make up today. Hmm... for being the world's "fastest growing religion," it sure has not grown much in the last 1162 years... and actually, compared to the percentages in the 7th Century, Islam has shrunk.