[HIPisTheAnswer]

Using 150k tonnes of above ground gold, if all of it was minted into currency, would equal +- 100M dollars. Probably not more than 10% is minted currency coins - .999 isn't for currency use. So there is about 10M dollars in existence.

[CompelTechnic]

1200 USD per ounce x 16 oz per lb x 2000 lb per ton x 150,000 =5.76E12 USD

5,760,000,000,000 USD, except for the fact that Troy ounces are slightly different than normal ounces. Too lazy to look up.

[HIPisTheAnswer]

a dollar is 24 3/4 grains of gold.

edit:typo

[CompelTechnic]

Ah I see.