How many Muslims are joining ISIS?

Caricature of ISIS (or DAESH, to Arabs) by Ibrahem Swaid, United Arab Emirates.
Caricature of ISIS (or DAESH, to Arabs) by Ibrahem Swaid, United Arab Emirates.

How many Muslims have gone to join the violent psychopaths of ISIS, or ISIL, or whatever we’re supposed to call it?

According to some, such as the ex-Muslim celebrity Ayaan Hirsi Ali, every Muslim is supposed to support ISIS. I mean, most Muslims are good people, but their religion is backward, tribal, and in need of “a reformation,” says the all-knowing Ms. Ali. She then speaks in moving terms of the peace she has found as an unbeliever.

Then there are the experts, many of whom wear their partisanship on their sleeves. Those that lean to the left insist that the “Islamic State” is neither Islamic nor a state, just a violent cult taking advantage of the complete breakdown of public order in Syria and much of Iraq. Maybe so, but these scholars seem reluctant to get specific about how many Muslims might belong to this cult.1

Meanwhile, scholars who lean to the right tend to toss out estimates that maybe 10 percent or less of the world’s Muslims are committed jihadists. While these estimates are far lower than the ones often bandied about on Facebook, they are also imprecise. It makes a big difference whether militant Muslims make up 1/100 or 1/10 of the total population.2

My own position, based on my experience as an American convert, has been that Muslims sympathetic to al-Qaeda and their ilk constitute about 1 percent of all the world’s Muslims, while those willing to actually go fight, rather than just talk about it, constitute about 1 percent of 1 percent, or 0.01%.

Worldwide, that still amounts to about 130,000 people. Pretty formidable if they were all gathered in the same spot.

Admittedly this (0.01%) was a very rough estimate, which I’ve used mainly to counteract routine overestimates. Anyway, I didn’t know of a way to test it.

Until now.

Getting an estimate

The rise of ISIS and the success of its gruesome social media campaign have put pressure on Western governments to track the number of Westerners, like “Jihadi John,” who join ISIS and take part in its brutal deeds.

The estimates are not perfect. Some government agencies only count known ISIS recruits, while others count everyone who went to Iraq or Syria as a “foreign fighter.” To my knowledge, only a few, like the British and Swedish intelligence services, have estimated how many nationals may have left the country to become “foreign fighters” without the government finding out about it.

I went with the numbers used in an interactive map published by Radio Free Europe/Radio Liberty. The numbers come from a range of official and media sources. I supplemented this map with figures from the Wikipedia article “Military of the Islamic State of Iraq and the Levant.”

Wherever the sources clashed, I went with the highest estimate of “number of foreign fighters.” Then, to allow for unknown recruits and potential future recruits, I multiplied the high estimate by 3.33. This is the factor that British intelligence used to estimate the probable total number of Islamist fighters from their country.4

The number of Muslims living in Western countries is also disputed. So I went with the numbers in a 2011 report by the Pew Research Center.3 I also refrained from adjusting those numbers for population growth between 2010 and 2015. (The average rate of Muslim population growth is estimated at 1.5 percent per year, slightly higher than the global average.) Here, too, I chose to make the model overestimate the proportion of Muslims who go abroad as foreign fighters.

Finally, I made no attempt to estimate how many ISIS recruits were responding to a 2014 appeal for “professionals,” such as doctors and engineers, to come serve the so-called caliphate. I did not try to guess how many recruits returned home again in short order. For argument’s sake, I assume that everyone on this list is a cold-blooded killer who knew exactly what he was getting into.

So, how great is the threat?


Foreign fighters with Islamist groups in Syria and Iraq amount to anywhere from 8/10 of 1 percent (0.8%) of New Zealand’s Muslim population, down to less than 1/10,000 of 1 percent of India’s. In general, the small Muslim minorities in Western countries turned up larger proportions than majority-Muslim countries.

I want to caution against reading too much into these numbers. Like FBI crime statistics, they should not be used to determine how serious the Muslim extremist threat is in one country as compared to another. They also contradict a finding (of the International Centre for the Study of Radicalisation and Political Violence) that Belgium has the highest number of foreign fighters per capita. I found higher estimates for Finland, Ireland, New Zealand, and Norway, though not in that order. These countries have some of the smallest Muslim minorities in the world, so all this really demonstrates is that a gang of a few hundred men makes a relatively large dent in a small community.

Note that these are deliberate overestimates that I arrived at by torturing the best data I could find. I am confident that the true level of radicalization is lower than these figures show and will remain so for the foreseeable future.

The median radicalization score for all countries was 0.03%, or 3 percent of 1 percent.5

For OECD countries, 0.10%.

For EU members, 0.09%.

For NATO members, 0.06%. (Canada, 0.05%; USA, 0.01%)

To put this in perspective: There are far more people in Western countries who believe that alien reptiles are running the world than there are people who have joined, or are prepared to join, ISIS or similar groups.


1 Juan Cole, Today’s Top 7 Myths about Daesh [ISIS], Feb. 17, 2015. This blog post includes an estimate of the proportion of British Muslims who volunteered for ISIS, but the figure is just tossed out as an aside, and the original post had a math error. 

2 For instance, Timothy R. Furnish, a professor at Georgia Perimeter College, suggested in 2005 that “jihadis” make up “perhaps somewhere between 1 and 10% of the world’s 1.3 billion Muslims.” That’s pretty vague! It’s also unclear whether that estimate includes another category of even scarier Muslims, “mahdists,” that Prof. Furnish believes in and likes to write about at his Mahdi Watch blog. 

3 Pew Research Center, The Future of the Global Muslim Population: Projections for 2010-2030, January 2011. Using a single source allows for more reliable comparison of populations in different countries, as estimates for each country will have been arrived at by identical or nearly identical methods. 

4 The British prime minister’s office has said that 600 Britons went to Syria or Iraq to join ISIS; the British intelligence estimate is up to 2,000. 

5 I was pleasantly surprised to notice that, before I applied the arbitrary “British intelligence” factor of 3.33, the median was 0.01%, or 1 percent of 1 percent. Exactly as I had guessed. A nice coincidence. 

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