That's not a great measure of wealth in the ancient world. The vast majority of economic transactions were carried out either in kind or in coin. Precious metals represented only a tiny sliver of any economy. Fortunately, archaeologists have made rough GDP estimates of many ancient empires, and we can make general comparisons.

Scheidel and Freissen (2009) put the per capita GDP of the Roman Empire in 150 AD at 620 1990 Dollars. Madisson (2001) puts the Han Chinese per capita GDP for the same period at 450 1990 Dollars. According to these figures, average Romans would have about 30% more purchasing power than average Han Chinese.

However, estimates vary. Sinologists like to point to things like widespread currency use to claim that China's economic performance exceeded what remaining records reflect.

The other two major contenders in terms of roughly contemporaneous economic powerhouses would be the Parthian Empire in modern Iran, and the Satavahana Dynasty in Central India. Unfortunately, very little exists in English on either of their economies. We know that both empires minted coinage in the Greek fashion, with images of rulers embossed on the face, but have little evidence to help construct even rudimentary economic models.