Here you can see how many Christians there are in the world, how many nonreligious people, how many Muslims, etc. The name of this website is Adherents.com. Technically, it's not an article. Nor is it a source on religions. It is stats on who believes what. This particular page was last modified April 19, 2007. It's listed on the Religious Studies website of the University of North Texas, so I know it is being monitored and is not a dead site, and since it is posted by a university department I figure it must be quality information.

All the same, adherents.com do not claim to have accurate figures; they suggest their figures are rather too high than too low. In other words, there are probably not more adherents to any given religion than their stats suggest.

Here are the top three categories:

1. Christianity: 2.1 billion
2. Islam: 1.3 billion
3. Secular/Nonreligious/Agnostic/Atheist: 1.1 billion

If there are seven billion people in the world today, well over half are either Christian, Islam, or nonreligious.

Here are the last four in a list of 22:

19. Neo-Paganism: 1 million
20. Unitarian-Universalism: 800 thousand
21. Rastafarianism: 600 thousand
22. Scientology: 500 thousand

Numbers 4-19 are all counted in the millions. The top three are counted by billions. Here is what the number "one billion" looks like: 1,000,000,000. It has nine zeros. The number "one million" has only six zeros. The number "one thousand" has only three zeros.

Thus, we need a thousand millions (1,000,000) to make one billion (1,000,000,000). That is an awful lot of people. There are a billion people who are not religious. HOWEVER, there are twice as many Christians in the world than nonreligious folk, and Islam is more than half the size of Christianity.

There is much more information on this website. Many links to more information. I would recommend it to a person who wants to learn about "religious geography" on a global level. As stated, it tells approximately how many people adhere to what religion world-wide. But it's only a rough estimate.