In a country of 1.3 billion people, it's no surprise that Chinese cities are huge. But just how big are they?

Recent figures released by Beijing's municipal bureau of statistics show that the capital's population grew by almost half a million residents in 2013 to 21.15 million. To put that in perspective, that's only slightly less than the entire population of Australia.

The figures were based on a survey the bureau conducted, which also found that the city is home to more than 8 million migrants, who make up about 40% of the population. The rest of the city's population, the bureau found, were hukou-toting residents—that is, those with official household registration papers entitling them to benefits like education and health care.

Figures released by Shanghai city authorities earlier this year showed that its population grew in 2013 by about 350,000 to reach 24.15 million—nearly the population of all of North Korea—including about 10 million migrants.

Technically, the most populous municipality in China is Chongqing, with a population of 29.7 million. But Chongqing, which contains vast swathes of countryside, covers an area roughly five times that of Beijing and 13 times that of Shanghai, and is more akin to a small province than a city.