It could be as high as 20 trillions US dollars,

otherwise the econimic scale of China cannot be explained at all with any theories or criteria! In terms of manufacturing sector, China is ~3 times the States. In 2009, China physical GDP (contributed by industry and agriculture) was bigger the sum of USA, Japs and Germany (see CIA World Factbook). This trend continues to 2015 and seems not to stop. In other words, China actual GDP in 2014 could be 30 to 35 trillions in US dollar if all economic activities in China was accounted! If this estimate is correct, then China 2014 GDP per capita in US dollar could be about 50% of the US count part, i.e., about $26,000. That makes much sense if you look at the annual electricity production data! (source: CIA World Factbook).