http://www.economist.com/blogs/graphicdetail/2013/11/chinese-and-american-gdp-forecasts
In December 2010 we introduced an interactive chart that allows you to make your own prediction of when China's economy will overtake America's. There are a variety of ways to compare economies. Our chart looks at their GDP in current dollars at market exchange rates. The timing of America's economic eclipse thus depends on five things: its own growth, China's growth, the evolution of prices in each country, and the exchange rate between them. If, for example, China's prices rise faster than America's, and its currency, the yuan, does not fall, then China's economy will be worth more, relative to America's, and it will overtake sooner.
In December 2010 we introduced an interactive chart that allows you to make your own prediction of when China's economy will overtake America's. There are a variety of ways to compare economies. Our chart looks at their GDP in current dollars at market exchange rates. The timing of America's economic eclipse thus depends on five things: its own growth, China's growth, the evolution of prices in each country, and the exchange rate between them. If, for example, China's prices rise faster than America's, and its currency, the yuan, does not fall, then China's economy will be worth more, relative to America's, and it will overtake sooner.