China and the UN have their own websites where this information can be found. I'll admit theres only roughly 1.4 Billion Atheists in the world , but according to every "stats" website I could find theres less than 900 million worldwide...Alot of atheists seem to be missing....Or in limbo...Or , simply religious groups would rather not count them at all. if you take the world population numbers and numbers reported internationally on "followers of religion" and atheists are only supposed to be 2.5%-20% even, that means alot of people out there are imaginary as christian , muslim , etc etc all added up still leaves an over 20% margin after calculation.

For instance the following is the rough numbers from the majority of websites out there.
1. Christianity: 2 billion
2. Islam: 1.3 billion
3. Hinduism: 900 million
4. Secular/Nonreligious/Agnostic/Atheist: 850 million
5. Buddhism: 360 million
6. Chinese traditional religion: 225 million(confucianism a philosphy not a religion)
7. primal-indigenous: 150 million
8. African Traditional & Diasporic: 95 million
9. Sikhism: 23 million
10. Juche: 19 million
11. Spiritism: 14 million
12. Judaism: 14 million
13. Baha'i: 6 million
14. Jainism: 4 million
15. Shinto: 4 million
16. Cao Dai: 3 million
17. Tenrikyo: 2.4 million
18. Neo-Paganism: 1 million(only a million people? Wiccan's would tend to disagree)
19. Unitarian-Universalism: 800 thousand
20. Rastafarianism: 700 thousand (we need more of these....especially considering the site were on )
21. Scientology: 600 thousand (only 600 thousand celebrities with too much money how weird?)
22. Zoroastrianism: 150 thousand

This as you can see still doesnt sum up the world population of roughly 6.4 billion In fact it goes below it , but I guess they skipped a few hundred million people and religions. Or decided not to count babies/toddlers etc which account for roughly 1/10 th of the world's pop also throwing this off (as they arent old enough to even know what religions is). Basically all this illustrates is don't believe everything you see online do the math yourself. Also realize that religions will always want to be on top. Also most of the sites claim either "declining" or "growing" each one that isnt governmental says "christianity" is growing, every government website says "falling" (as does every study done on the subject). So im inclined to find anything they report suspect. As would I be suspicious if someone reported Islam was the largest. But if it was actually supported by empirical evidence and not just over generalizations of the different sects then I would believe it. Suffice to say "christianity" only includes those that think of jesus as gods son and the messiah(by definition), which means many included with such arent actually christian at all...I'll admit I was wrong , but just assuming christianity is the biggest because of a few websites without digging deeper is just as "very very wrong" .