"How big is China?
Big. China is the world’s second largest economy. Based on PPP exchange rates, China increased from 6 percent of global output in 1995, to 15 percent last year (see chart). Or, if you prefer using market exchange rates, the corresponding rise in China’s share of global GDP is from 2 percent in 1995 to 12 percent in 2013.
When will China surpass the US? In 2018, based on PPP exchange rates. Later using market exchange rates—by 2019, the last year of our projections, China’s economy would be equivalent to about 64 percent of US GDP."