It's straightforward math, the hardest part is coming up with a width for China (I ended up using an approximation of 5,000 km), all of the other figures are on wikipedia (radius of Saturn's orbit, size of the milky way). Also, if you want to be super lazy you can get google to convert units for you:

https://www.google.com/search?ie=UTF-8&q=2.87+billion+km...